This article is about a geometric curve. For the term used in rhetoric, see Hyperbole.
In mathematics, a hyperbola (/haɪˈpɜːrbələ/ⓘ; pl. hyperbolas or hyperbolae/-liː/ⓘ; adj. hyperbolic/ˌhaɪpərˈbɒlɪk/ⓘ) is a type of smoothcurve lying in a plane, defined by its geometric properties or by equations for which it is the solution set. A hyperbola has two pieces, called connected components or branches, that are mirror images of each other and resemble two infinite bows. The hyperbola is one of the three kinds of conic section, formed by the intersection of a plane and a double cone. (The other conic sections are the parabola and the ellipse. A circle is a special case of an ellipse.) If the plane intersects both halves of the double cone but does not pass through the apex of the cones, then the conic is a hyperbola.
Besides being a conic section, a hyperbola can arise as the locus of points whose difference of distances to two fixed foci is constant, as a curve for each point of which the rays to two fixed foci are reflections across the tangent line at that point, or as the solution of certain bivariate quadratic equations such as the reciprocal relationship [1] In practical applications, a hyperbola can arise as the path followed by the shadow of the tip of a sundial's gnomon, the shape of an open orbit such as that of a celestial object exceeding the escape velocity of the nearest gravitational body, or the scattering trajectory of a subatomic particle, among others.
Each branch of the hyperbola has two arms which become straighter (lower curvature) further out from the center of the hyperbola. Diagonally opposite arms, one from each branch, tend in the limit to a common line, called the asymptote of those two arms. So there are two asymptotes, whose intersection is at the center of symmetry of the hyperbola, which can be thought of as the mirror point about which each branch reflects to form the other branch. In the case of the curve the asymptotes are the two coordinate axes.[2]
The word "hyperbola" derives from the Greekὑπερβολή, meaning "over-thrown" or "excessive", from which the English term hyperbole also derives. Hyperbolae were discovered by Menaechmus in his investigations of the problem of doubling the cube, but were then called sections of obtuse cones.[3] The term hyperbola is believed to have been coined by Apollonius of Perga (c. 262–c. 190 BC) in his definitive work on the conic sections, the Conics.[4] The names of the other two general conic sections, the ellipse and the parabola, derive from the corresponding Greek words for "deficient" and "applied"; all three names are borrowed from earlier Pythagorean terminology which referred to a comparison of the side of rectangles of fixed area with a given line segment. The rectangle could be "applied" to the segment (meaning, have an equal length), be shorter than the segment or exceed the segment.[5]
Definitionsedit
As locus of pointsedit
A hyperbola can be defined geometrically as a set of points (locus of points) in the Euclidean plane:
A hyperbola is a set of points, such that for any point of the set, the absolute difference of the distances to two fixed points (the foci) is constant, usually denoted by :[6]
The midpoint of the line segment joining the foci is called the center of the hyperbola.[7] The line through the foci is called the major axis. It contains the vertices, which have distance to the center. The distance of the foci to the center is called the focal distance or linear eccentricity. The quotient is the eccentricity.
The equation can be viewed in a different way (see diagram): If is the circle with midpoint and radius , then the distance of a point of the right branch to the circle equals the distance to the focus :
is called the circular directrix (related to focus ) of the hyperbola.[8][9] In order to get the left branch of the hyperbola, one has to use the circular directrix related to . This property should not be confused with the definition of a hyperbola with help of a directrix (line) below.
Hyperbola with equation y = A/xedit
If the xy-coordinate system is rotated about the origin by the angle and new coordinates are assigned, then . The rectangular hyperbola (whose semi-axes are equal) has the new equation . Solving for yields
Thus, in an xy-coordinate system the graph of a function with equation
is a rectangular hyperbola entirely in the first and third quadrants with
the coordinate axes as asymptotes,
the line as major axis ,
the center and the semi-axis
the vertices
the semi-latus rectum and radius of curvature at the vertices
the linear eccentricity and the eccentricity
the tangent at point
A rotation of the original hyperbola by results in a rectangular hyperbola entirely in the second and fourth quadrants, with the same asymptotes, center, semi-latus rectum, radius of curvature at the vertices, linear eccentricity, and eccentricity as for the case of rotation, with equation
the semi-axes
the line as major axis,
the vertices
Shifting the hyperbola with equation so that the new center is , yields the new equation
and the new asymptotes are and . The shape parameters remain unchanged.
By the directrix propertyedit
The two lines at distance from the center and parallel to the minor axis are called directrices of the hyperbola (see diagram).
For an arbitrary point of the hyperbola the quotient of the distance to one focus and to the corresponding directrix (see diagram) is equal to the eccentricity:
The proof for the pair follows from the fact that and satisfy the equation
The second case is proven analogously.
The inverse statement is also true and can be used to define a hyperbola (in a manner similar to the definition of a parabola):
For any point (focus), any line (directrix) not through and any real number with the set of points (locus of points), for which the quotient of the distances to the point and to the line is
Let and assume is a point on the curve. The directrix has equation . With , the relation produces the equations
and
The substitution yields
This is the equation of an ellipse () or a parabola () or a hyperbola (). All of these non-degenerate conics have, in common, the origin as a vertex (see diagram).
If , introduce new parameters so that , and then the equation above becomes
which is the equation of a hyperbola with center , the x-axis as major axis and the major/minor semi axis .
Construction of a directrixedit
Because of point of directrix (see diagram) and focus are inverse with respect to the circle inversion at circle (in diagram green). Hence point can be constructed using the theorem of Thales (not shown in the diagram). The directrix is the perpendicular to line through point .
Alternative construction of : Calculation shows, that point is the intersection of the asymptote with its perpendicular through (see diagram).
As plane section of a coneedit
The intersection of an upright double cone by a plane not through the vertex with slope greater than the slope of the lines on the cone is a hyperbola (see diagram: red curve). In order to prove the defining property of a hyperbola (see above) one uses two Dandelin spheres, which are spheres that touch the cone along circles , and the intersecting (hyperbola) plane at points and . It turns out: are the foci of the hyperbola.
Let be an arbitrary point of the intersection curve .
The generatrix of the cone containing intersects circle at point and circle at a point .
The line segments and are tangential to the sphere and, hence, are of equal length.
The line segments and are tangential to the sphere and, hence, are of equal length.
The result is: is independent of the hyperbola point , because no matter where point is, have to be on circles ,, and line segment has to cross the apex. Therefore, as point moves along the red curve (hyperbola), line segment simply rotates about apex without changing its length.
Pin and string constructionedit
The definition of a hyperbola by its foci and its circular directrices (see above) can be used for drawing an arc of it with help of pins, a string and a ruler:[10]
Choose the foci, the vertices and one of the circular directrices , for example (circle with radius )
A ruler is fixed at point free to rotate around . Point is marked at distance .
A string with length is prepared.
One end of the string is pinned at point on the ruler, the other end is pinned to point .
Take a pen and hold the string tight to the edge of the ruler.
Rotating the ruler around prompts the pen to draw an arc of the right branch of the hyperbola, because of (see the definition of a hyperbola by circular directrices).
Given two pencils of lines at two points (all lines containing and , respectively) and a projective but not perspective mapping of onto , then the intersection points of corresponding lines form a non-degenerate projective conic section.
For the generation of points of the hyperbola one uses the pencils at the vertices . Let be a point of the hyperbola and . The line segment is divided into n equally-spaced segments and this division is projected parallel with the diagonal as direction onto the line segment (see diagram). The parallel projection is part of the projective mapping between the pencils at and needed. The intersection points of any two related lines and are points of the uniquely defined hyperbola.
Remarks:
The subdivision could be extended beyond the points and in order to get more points, but the determination of the intersection points would become more inaccurate. A better idea is extending the points already constructed by symmetry (see animation).
The Steiner generation exists for ellipses and parabolas, too.
The Steiner generation is sometimes called a parallelogram method because one can use other points rather than the vertices, which starts with a parallelogram instead of a rectangle.
Inscribed angles for hyperbolas y = a/(x − b) + c and the 3-point-formedit
A hyperbola with equation is uniquely determined by three points with different x- and y-coordinates. A simple way to determine the shape parameters uses the inscribed angle theorem for hyperbolas:
In order to measure an angle between two lines with equations in this context one uses the quotient
Analogous to the inscribed angle theorem for circles one gets the
Inscribed angle theorem for hyperbolas[11][12] — For four points (see diagram) the following statement is true:
The four points are on a hyperbola with equation if and only if the angles at and are equal in the sense of the measurement above. That means if
The proof can be derived by straightforward calculation. If the points are on a hyperbola, one can assume the hyperbola's equation is .
A consequence of the inscribed angle theorem for hyperbolas is the
3-point-form of a hyperbola's equation — The equation of the hyperbola determined by 3 points is the solution of the equation
for .
As an affine image of the unit hyperbola x2 − y2 = 1edit
Any hyperbola is the affine image of the unit hyperbola with equation .
Parametric representationedit
An affine transformation of the Euclidean plane has the form , where is a regular matrix (its determinant is not 0) and is an arbitrary vector. If are the column vectors of the matrix , the unit hyperbola is mapped onto the hyperbola
is the center, a point of the hyperbola and a tangent vector at this point.
Verticesedit
In general the vectors are not perpendicular. That means, in general are not the vertices of the hyperbola. But point into the directions of the asymptotes. The tangent vector at point is
Because at a vertex the tangent is perpendicular to the major axis of the hyperbola one gets the parameter of a vertex from the equation
and hence from
which yields
The formulae ,, and were used.
The two vertices of the hyperbola are
Implicit representationedit
Solving the parametric representation for by Cramer's rule and using , one gets the implicit representation
Hyperbola in spaceedit
The definition of a hyperbola in this section gives a parametric representation of an arbitrary hyperbola, even in space, if one allows to be vectors in space.
As an affine image of the hyperbola y = 1/xedit
Because the unit hyperbola is affinely equivalent to the hyperbola , an arbitrary hyperbola can be considered as the affine image (see previous section) of the hyperbola :
is the center of the hyperbola, the vectors have the directions of the asymptotes and is a point of the hyperbola. The tangent vector is
At a vertex the tangent is perpendicular to the major axis. Hence
and the parameter of a vertex is
is equivalent to and are the vertices of the hyperbola.
The following properties of a hyperbola are easily proven using the representation of a hyperbola introduced in this section.
Tangent constructionedit
The tangent vector can be rewritten by factorization:
This means that
the diagonal of the parallelogram is parallel to the tangent at the hyperbola point (see diagram).
This property provides a way to construct the tangent at a point on the hyperbola.
This property of a hyperbola is an affine version of the 3-point-degeneration of Pascal's theorem.[13]
Area of the grey parallelogram
The area of the grey parallelogram in the above diagram is
and hence independent of point . The last equation follows from a calculation for the case, where is a vertex and the hyperbola in its canonical form
Point constructionedit
For a hyperbola with parametric representation (for simplicity the center is the origin) the following is true:
For any two points the points
are collinear with the center of the hyperbola (see diagram).
The simple proof is a consequence of the equation .
This property provides a possibility to construct points of a hyperbola if the asymptotes and one point are given.
This property of a hyperbola is an affine version of the 4-point-degeneration of Pascal's theorem.[14]
Tangent–asymptotes triangleedit
For simplicity the center of the hyperbola may be the origin and the vectors have equal length. If the last assumption is not fulfilled one can first apply a parameter transformation (see above) in order to make the assumption true. Hence are the vertices, span the minor axis and one gets and .
For the intersection points of the tangent at point with the asymptotes one gets the points
The area of the triangle can be calculated by a 2 × 2 determinant:
(see rules for determinants). is the area of the rhombus generated by . The area of a rhombus is equal to one half of the product of its diagonals. The diagonals are the semi-axes of the hyperbola. Hence:
The area of the triangle is independent of the point of the hyperbola:
Reciprocation of a circleedit
The reciprocation of a circleB in a circle C always yields a conic section such as a hyperbola. The process of "reciprocation in a circle C" consists of replacing every line and point in a geometrical figure with their corresponding pole and polar, respectively. The pole of a line is the inversion of its closest point to the circle C, whereas the polar of a point is the converse, namely, a line whose closest point to C is the inversion of the point.
The eccentricity of the conic section obtained by reciprocation is the ratio of the distances between the two circles' centers to the radius r of reciprocation circle C. If B and C represent the points at the centers of the corresponding circles, then
Since the eccentricity of a hyperbola is always greater than one, the center B must lie outside of the reciprocating circle C.
This definition implies that the hyperbola is both the locus of the poles of the tangent lines to the circle B, as well as the envelope of the polar lines of the points on B. Conversely, the circle B is the envelope of polars of points on the hyperbola, and the locus of poles of tangent lines to the hyperbola. Two tangent lines to B have no (finite) poles because they pass through the center C of the reciprocation circle C; the polars of the corresponding tangent points on B are the asymptotes of the hyperbola. The two branches of the hyperbola correspond to the two parts of the circle B that are separated by these tangent points.
Quadratic equationedit
A hyperbola can also be defined as a second-degree equation in the Cartesian coordinates in the plane,
provided that the constants and satisfy the determinant condition
This determinant is conventionally called the discriminant of the conic section.[15]
A special case of a hyperbola—the degenerate hyperbola consisting of two intersecting lines—occurs when another determinant is zero:
This determinant is sometimes called the discriminant of the conic section.[16]
The general equation's coefficients can be obtained from known semi-major axis semi-minor axis center coordinates , and rotation angle (the angle from the positive horizontal axis to the hyperbola's major axis) using the formulae:
These expressions can be derived from the canonical equation
hyperbola, this, article, about, geometric, curve, term, used, rhetoric, hyperbole, mathematics, hyperbola, ɜːr, hyperbolas, hyperbolae, hyperbolic, type, smooth, curve, lying, plane, defined, geometric, properties, equations, which, solution, hyperbola, piece. This article is about a geometric curve For the term used in rhetoric see Hyperbole In mathematics a hyperbola h aɪ ˈ p ɜːr b e l e pl hyperbolas or hyperbolae l iː adj hyperbolic ˌ h aɪ p er ˈ b ɒ l ɪ k is a type of smooth curve lying in a plane defined by its geometric properties or by equations for which it is the solution set A hyperbola has two pieces called connected components or branches that are mirror images of each other and resemble two infinite bows The hyperbola is one of the three kinds of conic section formed by the intersection of a plane and a double cone The other conic sections are the parabola and the ellipse A circle is a special case of an ellipse If the plane intersects both halves of the double cone but does not pass through the apex of the cones then the conic is a hyperbola A hyperbola is an open curve with two branches the intersection of a plane with both halves of a double cone The plane does not have to be parallel to the axis of the cone the hyperbola will be symmetrical in any case Hyperbola red features Besides being a conic section a hyperbola can arise as the locus of points whose difference of distances to two fixed foci is constant as a curve for each point of which the rays to two fixed foci are reflections across the tangent line at that point or as the solution of certain bivariate quadratic equations such as the reciprocal relationship x y 1 displaystyle xy 1 1 In practical applications a hyperbola can arise as the path followed by the shadow of the tip of a sundial s gnomon the shape of an open orbit such as that of a celestial object exceeding the escape velocity of the nearest gravitational body or the scattering trajectory of a subatomic particle among others Each branch of the hyperbola has two arms which become straighter lower curvature further out from the center of the hyperbola Diagonally opposite arms one from each branch tend in the limit to a common line called the asymptote of those two arms So there are two asymptotes whose intersection is at the center of symmetry of the hyperbola which can be thought of as the mirror point about which each branch reflects to form the other branch In the case of the curve y x 1 x displaystyle y x 1 x the asymptotes are the two coordinate axes 2 Hyperbolas share many of the ellipses analytical properties such as eccentricity focus and directrix Typically the correspondence can be made with nothing more than a change of sign in some term Many other mathematical objects have their origin in the hyperbola such as hyperbolic paraboloids saddle surfaces hyperboloids wastebaskets hyperbolic geometry Lobachevsky s celebrated non Euclidean geometry hyperbolic functions sinh cosh tanh etc and gyrovector spaces a geometry proposed for use in both relativity and quantum mechanics which is not Euclidean Contents 1 Etymology and history 2 Definitions 2 1 As locus of points 2 2 Hyperbola with equation y A x 2 3 By the directrix property 2 3 1 Proof 2 3 2 Construction of a directrix 2 4 As plane section of a cone 2 5 Pin and string construction 2 6 Steiner generation of a hyperbola 2 7 Inscribed angles for hyperbolas y a x b c and the 3 point form 2 8 As an affine image of the unit hyperbola x2 y2 1 2 8 1 Parametric representation 2 8 2 Vertices 2 8 3 Implicit representation 2 8 4 Hyperbola in space 2 9 As an affine image of the hyperbola y 1 x 2 9 1 Tangent construction 2 9 2 Point construction 2 9 3 Tangent asymptotes triangle 2 10 Reciprocation of a circle 2 11 Quadratic equation 3 In Cartesian coordinates 3 1 Equation 3 1 1 Eccentricity 3 2 Asymptotes 3 3 Semi latus rectum 3 4 Tangent 3 5 Rectangular hyperbola 3 6 Parametric representation with hyperbolic sine cosine 3 7 Conjugate hyperbola 4 In polar coordinates 4 1 Origin at the focus 4 2 Origin at the center 5 Parametric equations 6 Hyperbolic functions 7 Properties 7 1 Reflection property 7 2 Midpoints of parallel chords 7 3 Orthogonal tangents orthoptic 7 4 Pole polar relation for a hyperbola 7 5 Other properties 8 Arc length 9 Derived curves 10 Elliptic coordinates 11 Conic section analysis of the hyperbolic appearance of circles 12 Applications 12 1 Sundials 12 2 Multilateration 12 3 Path followed by a particle 12 4 Korteweg de Vries equation 12 5 Angle trisection 12 6 Efficient portfolio frontier 12 7 Biochemistry 13 Hyperbolas as plane sections of quadrics 14 See also 14 1 Other conic sections 14 2 Other related topics 15 Notes 16 References 17 External linksEtymology and history editThe word hyperbola derives from the Greek ὑperbolh meaning over thrown or excessive from which the English term hyperbole also derives Hyperbolae were discovered by Menaechmus in his investigations of the problem of doubling the cube but were then called sections of obtuse cones 3 The term hyperbola is believed to have been coined by Apollonius of Perga c 262 c 190 BC in his definitive work on the conic sections the Conics 4 The names of the other two general conic sections the ellipse and the parabola derive from the corresponding Greek words for deficient and applied all three names are borrowed from earlier Pythagorean terminology which referred to a comparison of the side of rectangles of fixed area with a given line segment The rectangle could be applied to the segment meaning have an equal length be shorter than the segment or exceed the segment 5 Definitions editAs locus of points edit nbsp Hyperbola definition by the distances of points to two fixed points foci nbsp Hyperbola definition with circular directrix A hyperbola can be defined geometrically as a set of points locus of points in the Euclidean plane A hyperbola is a set of points such that for any point P displaystyle P nbsp of the set the absolute difference of the distances P F 1 P F 2 displaystyle PF 1 PF 2 nbsp to two fixed points F 1 F 2 displaystyle F 1 F 2 nbsp the foci is constant usually denoted by 2 a a gt 0 displaystyle 2a a gt 0 nbsp 6 H P P F 2 P F 1 2 a displaystyle H left P left left PF 2 right left PF 1 right right 2a right nbsp The midpoint M displaystyle M nbsp of the line segment joining the foci is called the center of the hyperbola 7 The line through the foci is called the major axis It contains the vertices V 1 V 2 displaystyle V 1 V 2 nbsp which have distance a displaystyle a nbsp to the center The distance c displaystyle c nbsp of the foci to the center is called the focal distance or linear eccentricity The quotient c a displaystyle tfrac c a nbsp is the eccentricity e displaystyle e nbsp The equation P F 2 P F 1 2 a displaystyle left left PF 2 right left PF 1 right right 2a nbsp can be viewed in a different way see diagram If c 2 displaystyle c 2 nbsp is the circle with midpoint F 2 displaystyle F 2 nbsp and radius 2 a displaystyle 2a nbsp then the distance of a point P displaystyle P nbsp of the right branch to the circle c 2 displaystyle c 2 nbsp equals the distance to the focus F 1 displaystyle F 1 nbsp P F 1 P c 2 displaystyle PF 1 Pc 2 nbsp c 2 displaystyle c 2 nbsp is called the circular directrix related to focus F 2 displaystyle F 2 nbsp of the hyperbola 8 9 In order to get the left branch of the hyperbola one has to use the circular directrix related to F 1 displaystyle F 1 nbsp This property should not be confused with the definition of a hyperbola with help of a directrix line below Hyperbola with equation y A x edit nbsp Rotating the coordinate system in order to describe a rectangular hyperbola as graph of a function nbsp Three rectangular hyperbolas y A x displaystyle y A x nbsp with the coordinate axes as asymptotes red A 1 magenta A 4 blue A 9 If the xy coordinate system is rotated about the origin by the angle 45 displaystyle 45 circ nbsp and new coordinates 3 h displaystyle xi eta nbsp are assigned then x 3 h 2 y 3 h 2 displaystyle x tfrac xi eta sqrt 2 y tfrac xi eta sqrt 2 nbsp The rectangular hyperbola x 2 y 2 a 2 1 displaystyle tfrac x 2 y 2 a 2 1 nbsp whose semi axes are equal has the new equation 2 3 h a 2 1 displaystyle tfrac 2 xi eta a 2 1 nbsp Solving for h displaystyle eta nbsp yields h a 2 2 3 displaystyle eta tfrac a 2 2 xi nbsp Thus in an xy coordinate system the graph of a function f x A x A gt 0 displaystyle f x mapsto tfrac A x A gt 0 nbsp with equationy A x A gt 0 displaystyle y frac A x A gt 0 nbsp is a rectangular hyperbola entirely in the first and third quadrants with the coordinate axes as asymptotes the line y x displaystyle y x nbsp as major axis the center 0 0 displaystyle 0 0 nbsp and the semi axis a b 2 A displaystyle a b sqrt 2A nbsp the vertices A A A A displaystyle left sqrt A sqrt A right left sqrt A sqrt A right nbsp the semi latus rectum and radius of curvature at the vertices p a 2 A displaystyle p a sqrt 2A nbsp the linear eccentricity c 2 A displaystyle c 2 sqrt A nbsp and the eccentricity e 2 displaystyle e sqrt 2 nbsp the tangent y A x 0 2 x 2 A x 0 displaystyle y tfrac A x 0 2 x 2 tfrac A x 0 nbsp at point x 0 A x 0 displaystyle x 0 A x 0 nbsp A rotation of the original hyperbola by 45 displaystyle 45 circ nbsp results in a rectangular hyperbola entirely in the second and fourth quadrants with the same asymptotes center semi latus rectum radius of curvature at the vertices linear eccentricity and eccentricity as for the case of 45 displaystyle 45 circ nbsp rotation with equationy A x A gt 0 displaystyle y frac A x A gt 0 nbsp the semi axes a b 2 A displaystyle a b sqrt 2A nbsp the line y x displaystyle y x nbsp as major axis the vertices A A A A displaystyle left sqrt A sqrt A right left sqrt A sqrt A right nbsp Shifting the hyperbola with equation y A x A 0 displaystyle y frac A x A neq 0 nbsp so that the new center is c 0 d 0 displaystyle c 0 d 0 nbsp yields the new equationy A x c 0 d 0 displaystyle y frac A x c 0 d 0 nbsp and the new asymptotes are x c 0 displaystyle x c 0 nbsp and y d 0 displaystyle y d 0 nbsp The shape parameters a b p c e displaystyle a b p c e nbsp remain unchanged By the directrix property edit nbsp Hyperbola directrix property nbsp Hyperbola definition with directrix property The two lines at distance d a 2 c textstyle d frac a 2 c nbsp from the center and parallel to the minor axis are called directrices of the hyperbola see diagram For an arbitrary point P displaystyle P nbsp of the hyperbola the quotient of the distance to one focus and to the corresponding directrix see diagram is equal to the eccentricity P F 1 P l 1 P F 2 P l 2 e c a displaystyle frac PF 1 Pl 1 frac PF 2 Pl 2 e frac c a nbsp The proof for the pair F 1 l 1 displaystyle F 1 l 1 nbsp follows from the fact that P F 1 2 x c 2 y 2 P l 1 2 x a 2 c 2 displaystyle PF 1 2 x c 2 y 2 Pl 1 2 left x tfrac a 2 c right 2 nbsp and y 2 b 2 a 2 x 2 b 2 displaystyle y 2 tfrac b 2 a 2 x 2 b 2 nbsp satisfy the equation P F 1 2 c 2 a 2 P l 1 2 0 displaystyle PF 1 2 frac c 2 a 2 Pl 1 2 0 nbsp The second case is proven analogously nbsp Pencil of conics with a common vertex and common semi latus rectum The inverse statement is also true and can be used to define a hyperbola in a manner similar to the definition of a parabola For any point F displaystyle F nbsp focus any line l displaystyle l nbsp directrix not through F displaystyle F nbsp and any real number e displaystyle e nbsp with e gt 1 displaystyle e gt 1 nbsp the set of points locus of points for which the quotient of the distances to the point and to the line is e displaystyle e nbsp H P P F P l e displaystyle H left P Biggr frac PF Pl e right nbsp is a hyperbola The choice e 1 displaystyle e 1 nbsp yields a parabola and if e lt 1 displaystyle e lt 1 nbsp an ellipse Proof edit Let F f 0 e gt 0 displaystyle F f 0 e gt 0 nbsp and assume 0 0 displaystyle 0 0 nbsp is a point on the curve The directrix l displaystyle l nbsp has equation x f e displaystyle x tfrac f e nbsp With P x y displaystyle P x y nbsp the relation P F 2 e 2 P l 2 displaystyle PF 2 e 2 Pl 2 nbsp produces the equations x f 2 y 2 e 2 x f e 2 e x f 2 displaystyle x f 2 y 2 e 2 left x tfrac f e right 2 ex f 2 nbsp and x 2 e 2 1 2 x f 1 e y 2 0 displaystyle x 2 e 2 1 2xf 1 e y 2 0 nbsp The substitution p f 1 e displaystyle p f 1 e nbsp yieldsx 2 e 2 1 2 p x y 2 0 displaystyle x 2 e 2 1 2px y 2 0 nbsp This is the equation of an ellipse e lt 1 displaystyle e lt 1 nbsp or a parabola e 1 displaystyle e 1 nbsp or a hyperbola e gt 1 displaystyle e gt 1 nbsp All of these non degenerate conics have in common the origin as a vertex see diagram If e gt 1 displaystyle e gt 1 nbsp introduce new parameters a b displaystyle a b nbsp so that e 2 1 b 2 a 2 and p b 2 a displaystyle e 2 1 tfrac b 2 a 2 text and p tfrac b 2 a nbsp and then the equation above becomes x a 2 a 2 y 2 b 2 1 displaystyle frac x a 2 a 2 frac y 2 b 2 1 nbsp which is the equation of a hyperbola with center a 0 displaystyle a 0 nbsp the x axis as major axis and the major minor semi axis a b displaystyle a b nbsp nbsp Hyperbola construction of a directrix Construction of a directrix edit Because of c a 2 c a 2 displaystyle c cdot tfrac a 2 c a 2 nbsp point L 1 displaystyle L 1 nbsp of directrix l 1 displaystyle l 1 nbsp see diagram and focus F 1 displaystyle F 1 nbsp are inverse with respect to the circle inversion at circle x 2 y 2 a 2 displaystyle x 2 y 2 a 2 nbsp in diagram green Hence point E 1 displaystyle E 1 nbsp can be constructed using the theorem of Thales not shown in the diagram The directrix l 1 displaystyle l 1 nbsp is the perpendicular to line F 1 F 2 displaystyle overline F 1 F 2 nbsp through point E 1 displaystyle E 1 nbsp Alternative construction of E 1 displaystyle E 1 nbsp Calculation shows that point E 1 displaystyle E 1 nbsp is the intersection of the asymptote with its perpendicular through F 1 displaystyle F 1 nbsp see diagram As plane section of a cone edit nbsp Hyperbola red two views of a cone and two Dandelin spheres d1 d2 The intersection of an upright double cone by a plane not through the vertex with slope greater than the slope of the lines on the cone is a hyperbola see diagram red curve In order to prove the defining property of a hyperbola see above one uses two Dandelin spheres d 1 d 2 displaystyle d 1 d 2 nbsp which are spheres that touch the cone along circles c 1 displaystyle c 1 nbsp c 2 displaystyle c 2 nbsp and the intersecting hyperbola plane at points F 1 displaystyle F 1 nbsp and F 2 displaystyle F 2 nbsp It turns out F 1 F 2 displaystyle F 1 F 2 nbsp are the foci of the hyperbola Let P displaystyle P nbsp be an arbitrary point of the intersection curve The generatrix of the cone containing P displaystyle P nbsp intersects circle c 1 displaystyle c 1 nbsp at point A displaystyle A nbsp and circle c 2 displaystyle c 2 nbsp at a point B displaystyle B nbsp The line segments P F 1 displaystyle overline PF 1 nbsp and P A displaystyle overline PA nbsp are tangential to the sphere d 1 displaystyle d 1 nbsp and hence are of equal length The line segments P F 2 displaystyle overline PF 2 nbsp and P B displaystyle overline PB nbsp are tangential to the sphere d 2 displaystyle d 2 nbsp and hence are of equal length The result is P F 1 P F 2 P A P B A B displaystyle PF 1 PF 2 PA PB AB nbsp is independent of the hyperbola point P displaystyle P nbsp because no matter where point P displaystyle P nbsp is A B displaystyle A B nbsp have to be on circles c 1 displaystyle c 1 nbsp c 2 displaystyle c 2 nbsp and line segment A B displaystyle AB nbsp has to cross the apex Therefore as point P displaystyle P nbsp moves along the red curve hyperbola line segment A B displaystyle overline AB nbsp simply rotates about apex without changing its length Pin and string construction edit nbsp Hyperbola Pin and string construction The definition of a hyperbola by its foci and its circular directrices see above can be used for drawing an arc of it with help of pins a string and a ruler 10 Choose the foci F 1 F 2 displaystyle F 1 F 2 nbsp the vertices V 1 V 2 displaystyle V 1 V 2 nbsp and one of the circular directrices for example c 2 displaystyle c 2 nbsp circle with radius 2 a displaystyle 2a nbsp A ruler is fixed at point F 2 displaystyle F 2 nbsp free to rotate around F 2 displaystyle F 2 nbsp Point B displaystyle B nbsp is marked at distance 2 a displaystyle 2a nbsp A string with length A B displaystyle AB nbsp is prepared One end of the string is pinned at point A displaystyle A nbsp on the ruler the other end is pinned to point F 1 displaystyle F 1 nbsp Take a pen and hold the string tight to the edge of the ruler Rotating the ruler around F 2 displaystyle F 2 nbsp prompts the pen to draw an arc of the right branch of the hyperbola because of P F 1 P B displaystyle PF 1 PB nbsp see the definition of a hyperbola by circular directrices Steiner generation of a hyperbola edit nbsp Hyperbola Steiner generation nbsp Hyperbola y 1 x Steiner generation The following method to construct single points of a hyperbola relies on the Steiner generation of a non degenerate conic section Given two pencils B U B V displaystyle B U B V nbsp of lines at two points U V displaystyle U V nbsp all lines containing U displaystyle U nbsp and V displaystyle V nbsp respectively and a projective but not perspective mapping p displaystyle pi nbsp of B U displaystyle B U nbsp onto B V displaystyle B V nbsp then the intersection points of corresponding lines form a non degenerate projective conic section For the generation of points of the hyperbola x 2 a 2 y 2 b 2 1 displaystyle tfrac x 2 a 2 tfrac y 2 b 2 1 nbsp one uses the pencils at the vertices V 1 V 2 displaystyle V 1 V 2 nbsp Let P x 0 y 0 displaystyle P x 0 y 0 nbsp be a point of the hyperbola and A a y 0 B x 0 0 displaystyle A a y 0 B x 0 0 nbsp The line segment B P displaystyle overline BP nbsp is divided into n equally spaced segments and this division is projected parallel with the diagonal A B displaystyle AB nbsp as direction onto the line segment A P displaystyle overline AP nbsp see diagram The parallel projection is part of the projective mapping between the pencils at V 1 displaystyle V 1 nbsp and V 2 displaystyle V 2 nbsp needed The intersection points of any two related lines S 1 A i displaystyle S 1 A i nbsp and S 2 B i displaystyle S 2 B i nbsp are points of the uniquely defined hyperbola Remarks The subdivision could be extended beyond the points A displaystyle A nbsp and B displaystyle B nbsp in order to get more points but the determination of the intersection points would become more inaccurate A better idea is extending the points already constructed by symmetry see animation The Steiner generation exists for ellipses and parabolas too The Steiner generation is sometimes called a parallelogram method because one can use other points rather than the vertices which starts with a parallelogram instead of a rectangle Inscribed angles for hyperbolas y a x b c and the 3 point form edit nbsp Hyperbola inscribed angle theorem A hyperbola with equation y a x b c a 0 displaystyle y tfrac a x b c a neq 0 nbsp is uniquely determined by three points x 1 y 1 x 2 y 2 x 3 y 3 displaystyle x 1 y 1 x 2 y 2 x 3 y 3 nbsp with different x and y coordinates A simple way to determine the shape parameters a b c displaystyle a b c nbsp uses the inscribed angle theorem for hyperbolas In order to measure an angle between two lines with equations y m 1 x d 1 y m 2 x d 2 m 1 m 2 0 displaystyle y m 1 x d 1 y m 2 x d 2 m 1 m 2 neq 0 nbsp in this context one uses the quotient m 1 m 2 displaystyle frac m 1 m 2 nbsp Analogous to the inscribed angle theorem for circles one gets the Inscribed angle theorem for hyperbolas 11 12 For four points P i x i y i i 1 2 3 4 x i x k y i y k i k displaystyle P i x i y i i 1 2 3 4 x i neq x k y i neq y k i neq k nbsp see diagram the following statement is true The four points are on a hyperbola with equation y a x b c displaystyle y tfrac a x b c nbsp if and only if the angles at P 3 displaystyle P 3 nbsp and P 4 displaystyle P 4 nbsp are equal in the sense of the measurement above That means if y 4 y 1 x 4 x 1 x 4 x 2 y 4 y 2 y 3 y 1 x 3 x 1 x 3 x 2 y 3 y 2 displaystyle frac y 4 y 1 x 4 x 1 frac x 4 x 2 y 4 y 2 frac y 3 y 1 x 3 x 1 frac x 3 x 2 y 3 y 2 nbsp The proof can be derived by straightforward calculation If the points are on a hyperbola one can assume the hyperbola s equation is y a x displaystyle y a x nbsp A consequence of the inscribed angle theorem for hyperbolas is the 3 point form of a hyperbola s equation The equation of the hyperbola determined by 3 points P i x i y i i 1 2 3 x i x k y i y k i k displaystyle P i x i y i i 1 2 3 x i neq x k y i neq y k i neq k nbsp is the solution of the equation y y 1 x x 1 x x 2 y y 2 y 3 y 1 x 3 x 1 x 3 x 2 y 3 y 2 displaystyle frac color red y y 1 color green x x 1 frac color green x x 2 color red y y 2 frac y 3 y 1 x 3 x 1 frac x 3 x 2 y 3 y 2 nbsp for y displaystyle color red y nbsp As an affine image of the unit hyperbola x2 y2 1 edit nbsp Hyperbola as an affine image of the unit hyperbola Another definition of a hyperbola uses affine transformations Any hyperbola is the affine image of the unit hyperbola with equation x 2 y 2 1 displaystyle x 2 y 2 1 nbsp Parametric representation edit An affine transformation of the Euclidean plane has the form x f 0 A x displaystyle vec x to vec f 0 A vec x nbsp where A displaystyle A nbsp is a regular matrix its determinant is not 0 and f 0 displaystyle vec f 0 nbsp is an arbitrary vector If f 1 f 2 displaystyle vec f 1 vec f 2 nbsp are the column vectors of the matrix A displaystyle A nbsp the unit hyperbola cosh t sinh t t R displaystyle pm cosh t sinh t t in mathbb R nbsp is mapped onto the hyperbolax p t f 0 f 1 cosh t f 2 sinh t displaystyle vec x vec p t vec f 0 pm vec f 1 cosh t vec f 2 sinh t nbsp f 0 displaystyle vec f 0 nbsp is the center f 0 f 1 displaystyle vec f 0 vec f 1 nbsp a point of the hyperbola and f 2 displaystyle vec f 2 nbsp a tangent vector at this point Vertices edit In general the vectors f 1 f 2 displaystyle vec f 1 vec f 2 nbsp are not perpendicular That means in general f 0 f 1 displaystyle vec f 0 pm vec f 1 nbsp are not the vertices of the hyperbola But f 1 f 2 displaystyle vec f 1 pm vec f 2 nbsp point into the directions of the asymptotes The tangent vector at point p t displaystyle vec p t nbsp isp t f 1 sinh t f 2 cosh t displaystyle vec p t vec f 1 sinh t vec f 2 cosh t nbsp Because at a vertex the tangent is perpendicular to the major axis of the hyperbola one gets the parameter t 0 displaystyle t 0 nbsp of a vertex from the equation p t p t f 0 f 1 sinh t f 2 cosh t f 1 cosh t f 2 sinh t 0 displaystyle vec p t cdot left vec p t vec f 0 right left vec f 1 sinh t vec f 2 cosh t right cdot left vec f 1 cosh t vec f 2 sinh t right 0 nbsp and hence from coth 2 t 0 f 1 2 f 2 2 2 f 1 f 2 displaystyle coth 2t 0 tfrac vec f 1 2 vec f 2 2 2 vec f 1 cdot vec f 2 nbsp which yields t 0 1 4 ln f 1 f 2 2 f 1 f 2 2 displaystyle t 0 tfrac 1 4 ln tfrac left vec f 1 vec f 2 right 2 left vec f 1 vec f 2 right 2 nbsp The formulae cosh 2 x sinh 2 x cosh 2 x displaystyle cosh 2 x sinh 2 x cosh 2x nbsp 2 sinh x cosh x sinh 2 x displaystyle 2 sinh x cosh x sinh 2x nbsp and arcoth x 1 2 ln x 1 x 1 displaystyle operatorname arcoth x tfrac 1 2 ln tfrac x 1 x 1 nbsp were used The two vertices of the hyperbola are f 0 f 1 cosh t 0 f 2 sinh t 0 displaystyle vec f 0 pm left vec f 1 cosh t 0 vec f 2 sinh t 0 right nbsp Implicit representation edit Solving the parametric representation for cosh t sinh t displaystyle cosh t sinh t nbsp by Cramer s rule and using cosh 2 t sinh 2 t 1 0 displaystyle cosh 2 t sinh 2 t 1 0 nbsp one gets the implicit representationdet x f 0 f 2 2 det f 1 x f 0 2 det f 1 f 2 2 0 displaystyle det left vec x vec f 0 vec f 2 right 2 det left vec f 1 vec x vec f 0 right 2 det left vec f 1 vec f 2 right 2 0 nbsp Hyperbola in space edit The definition of a hyperbola in this section gives a parametric representation of an arbitrary hyperbola even in space if one allows f 0 f 1 f 2 displaystyle vec f 0 vec f 1 vec f 2 nbsp to be vectors in space As an affine image of the hyperbola y 1 x edit nbsp Hyperbola as affine image of y 1 x Because the unit hyperbola x 2 y 2 1 displaystyle x 2 y 2 1 nbsp is affinely equivalent to the hyperbola y 1 x displaystyle y 1 x nbsp an arbitrary hyperbola can be considered as the affine image see previous section of the hyperbola y 1 x displaystyle y 1 x nbsp x p t f 0 f 1 t f 2 1 t t 0 displaystyle vec x vec p t vec f 0 vec f 1 t vec f 2 tfrac 1 t quad t neq 0 nbsp M f 0 displaystyle M vec f 0 nbsp is the center of the hyperbola the vectors f 1 f 2 displaystyle vec f 1 vec f 2 nbsp have the directions of the asymptotes and f 1 f 2 displaystyle vec f 1 vec f 2 nbsp is a point of the hyperbola The tangent vector isp t f 1 f 2 1 t 2 displaystyle vec p t vec f 1 vec f 2 tfrac 1 t 2 nbsp At a vertex the tangent is perpendicular to the major axis Hence p t p t f 0 f 1 f 2 1 t 2 f 1 t f 2 1 t f 1 2 t f 2 2 1 t 3 0 displaystyle vec p t cdot left vec p t vec f 0 right left vec f 1 vec f 2 tfrac 1 t 2 right cdot left vec f 1 t vec f 2 tfrac 1 t right vec f 1 2 t vec f 2 2 tfrac 1 t 3 0 nbsp and the parameter of a vertex is t 0 f 2 2 f 1 2 4 displaystyle t 0 pm sqrt 4 frac vec f 2 2 vec f 1 2 nbsp f 1 f 2 displaystyle left vec f 1 right left vec f 2 right nbsp is equivalent to t 0 1 displaystyle t 0 pm 1 nbsp and f 0 f 1 f 2 displaystyle vec f 0 pm vec f 1 vec f 2 nbsp are the vertices of the hyperbola The following properties of a hyperbola are easily proven using the representation of a hyperbola introduced in this section Tangent construction edit nbsp Tangent construction asymptotes and P given tangent The tangent vector can be rewritten by factorization p t 1 t f 1 t f 2 1 t displaystyle vec p t tfrac 1 t left vec f 1 t vec f 2 tfrac 1 t right nbsp This means that the diagonal A B displaystyle AB nbsp of the parallelogram M f 0 A f 0 f 1 t B f 0 f 2 1 t P f 0 f 1 t f 2 1 t displaystyle M vec f 0 A vec f 0 vec f 1 t B vec f 0 vec f 2 tfrac 1 t P vec f 0 vec f 1 t vec f 2 tfrac 1 t nbsp is parallel to the tangent at the hyperbola point P displaystyle P nbsp see diagram This property provides a way to construct the tangent at a point on the hyperbola This property of a hyperbola is an affine version of the 3 point degeneration of Pascal s theorem 13 Area of the grey parallelogram The area of the grey parallelogram M A P B displaystyle MAPB nbsp in the above diagram isArea det t f 1 1 t f 2 det f 1 f 2 a 2 b 2 4 displaystyle text Area left det left t vec f 1 tfrac 1 t vec f 2 right right left det left vec f 1 vec f 2 right right cdots frac a 2 b 2 4 nbsp and hence independent of point P displaystyle P nbsp The last equation follows from a calculation for the case where P displaystyle P nbsp is a vertex and the hyperbola in its canonical form x 2 a 2 y 2 b 2 1 displaystyle tfrac x 2 a 2 tfrac y 2 b 2 1 nbsp Point construction edit nbsp Point construction asymptotes and P1 are given P2 For a hyperbola with parametric representation x p t f 1 t f 2 1 t displaystyle vec x vec p t vec f 1 t vec f 2 tfrac 1 t nbsp for simplicity the center is the origin the following is true For any two points P 1 f 1 t 1 f 2 1 t 1 P 2 f 1 t 2 f 2 1 t 2 displaystyle P 1 vec f 1 t 1 vec f 2 tfrac 1 t 1 P 2 vec f 1 t 2 vec f 2 tfrac 1 t 2 nbsp the points A a f 1 t 1 f 2 1 t 2 B b f 1 t 2 f 2 1 t 1 displaystyle A vec a vec f 1 t 1 vec f 2 tfrac 1 t 2 B vec b vec f 1 t 2 vec f 2 tfrac 1 t 1 nbsp are collinear with the center of the hyperbola see diagram The simple proof is a consequence of the equation 1 t 1 a 1 t 2 b displaystyle tfrac 1 t 1 vec a tfrac 1 t 2 vec b nbsp This property provides a possibility to construct points of a hyperbola if the asymptotes and one point are given This property of a hyperbola is an affine version of the 4 point degeneration of Pascal s theorem 14 Tangent asymptotes triangle edit nbsp Hyperbola tangent asymptotes triangle For simplicity the center of the hyperbola may be the origin and the vectors f 1 f 2 displaystyle vec f 1 vec f 2 nbsp have equal length If the last assumption is not fulfilled one can first apply a parameter transformation see above in order to make the assumption true Hence f 1 f 2 displaystyle pm vec f 1 vec f 2 nbsp are the vertices f 1 f 2 displaystyle pm vec f 1 vec f 2 nbsp span the minor axis and one gets f 1 f 2 a displaystyle vec f 1 vec f 2 a nbsp and f 1 f 2 b displaystyle vec f 1 vec f 2 b nbsp For the intersection points of the tangent at point p t 0 f 1 t 0 f 2 1 t 0 displaystyle vec p t 0 vec f 1 t 0 vec f 2 tfrac 1 t 0 nbsp with the asymptotes one gets the pointsC 2 t 0 f 1 D 2 t 0 f 2 displaystyle C 2t 0 vec f 1 D tfrac 2 t 0 vec f 2 nbsp The area of the triangle M C D displaystyle M C D nbsp can be calculated by a 2 2 determinant A 1 2 det 2 t 0 f 1 2 t 0 f 2 2 det f 1 f 2 displaystyle A tfrac 1 2 Big det left 2t 0 vec f 1 tfrac 2 t 0 vec f 2 right Big 2 Big det left vec f 1 vec f 2 right Big nbsp see rules for determinants det f 1 f 2 displaystyle left det vec f 1 vec f 2 right nbsp is the area of the rhombus generated by f 1 f 2 displaystyle vec f 1 vec f 2 nbsp The area of a rhombus is equal to one half of the product of its diagonals The diagonals are the semi axes a b displaystyle a b nbsp of the hyperbola Hence The area of the triangle M C D displaystyle MCD nbsp is independent of the point of the hyperbola A a b displaystyle A ab nbsp Reciprocation of a circle edit The reciprocation of a circle B in a circle C always yields a conic section such as a hyperbola The process of reciprocation in a circle C consists of replacing every line and point in a geometrical figure with their corresponding pole and polar respectively The pole of a line is the inversion of its closest point to the circle C whereas the polar of a point is the converse namely a line whose closest point to C is the inversion of the point The eccentricity of the conic section obtained by reciprocation is the ratio of the distances between the two circles centers to the radius r of reciprocation circle C If B and C represent the points at the centers of the corresponding circles thene B C r displaystyle e frac overline BC r nbsp Since the eccentricity of a hyperbola is always greater than one the center B must lie outside of the reciprocating circle C This definition implies that the hyperbola is both the locus of the poles of the tangent lines to the circle B as well as the envelope of the polar lines of the points on B Conversely the circle B is the envelope of polars of points on the hyperbola and the locus of poles of tangent lines to the hyperbola Two tangent lines to B have no finite poles because they pass through the center C of the reciprocation circle C the polars of the corresponding tangent points on B are the asymptotes of the hyperbola The two branches of the hyperbola correspond to the two parts of the circle B that are separated by these tangent points Quadratic equation edit A hyperbola can also be defined as a second degree equation in the Cartesian coordinates x y displaystyle x y nbsp in the plane A x x x 2 2 A x y x y A y y y 2 2 B x x 2 B y y C 0 displaystyle A xx x 2 2A xy xy A yy y 2 2B x x 2B y y C 0 nbsp provided that the constants A x x displaystyle A xx nbsp A x y displaystyle A xy nbsp A y y displaystyle A yy nbsp B x displaystyle B x nbsp B y displaystyle B y nbsp and C displaystyle C nbsp satisfy the determinant conditionD A x x A x y A x y A y y lt 0 displaystyle D begin vmatrix A xx amp A xy A xy amp A yy end vmatrix lt 0 nbsp This determinant is conventionally called the discriminant of the conic section 15 A special case of a hyperbola the degenerate hyperbola consisting of two intersecting lines occurs when another determinant is zero D A x x A x y B x A x y A y y B y B x B y C 0 displaystyle Delta begin vmatrix A xx amp A xy amp B x A xy amp A yy amp B y B x amp B y amp C end vmatrix 0 nbsp This determinant D displaystyle Delta nbsp is sometimes called the discriminant of the conic section 16 The general equation s coefficients can be obtained from known semi major axis a displaystyle a nbsp semi minor axis b displaystyle b nbsp center coordinates x y displaystyle x circ y circ nbsp and rotation angle 8 displaystyle theta nbsp the angle from the positive horizontal axis to the hyperbola s major axis using the formulae A x x a 2 sin 2 8 b 2 cos 2 8 B x A x x x A x y y A y y a 2 cos 2 8 b 2 sin 2 8 B y A x y x A y y y A x y a 2 b 2 sin 8 cos 8 C A x x x 2 2 A x y x y A y y y 2 a 2 b 2 displaystyle begin aligned A xx amp a 2 sin 2 theta b 2 cos 2 theta amp B x amp A xx x circ A xy y circ 1ex A yy amp a 2 cos 2 theta b 2 sin 2 theta amp B y amp A xy x circ A yy y circ 1ex A xy amp left a 2 b 2 right sin theta cos theta amp C amp A xx x circ 2 2A xy x circ y circ A yy y circ 2 a 2 b 2 end aligned nbsp These expressions can be derived from the canonical equationX 2 a 2 Y 2 b 2 1 displaystyle frac X 2 a 2 frac Y 2 b 2 1 nbsp by a translation and rotation of the coordinates x y displaystyle x y nbsp X x x cos 8 y y sin 8 Y x x sin 8 y y cos 8 displaystyle begin alignedat 2 X amp phantom left x x circ right cos theta amp amp left y y circ right sin theta Y amp left x x circ right sin theta amp amp left y y circ right cos theta end alignedat nbsp Given the above general parametrization of the hyperbola in Cartesian coordinates the eccentricity can be found using the formula in Conic section Eccentricity in terms of coefficients The center x c y c displaystyle x c y c nbsp of the hyperbola may be determined from the formulaex c 1 D B x A x y B y A y y y c 1 D A x x B x A x y B y displaystyle begin aligned x c amp frac 1 D begin vmatrix B x amp A xy B y amp A yy end vmatrix 1ex y c amp frac 1 D begin vmatrix A xx amp B x A xy amp B y end vmatrix end aligned nbsp In terms of new coordinates 3 x x c displaystyle xi x x c nbsp and h y y c displaystyle eta y y c nbsp the defining equation of the hyperbola can be writtenA x x 3 2 2 A x y 3 h A y y h 2 D D 0 displaystyle A xx xi 2 2A xy xi eta A yy eta 2 frac Delta D 0 nbsp The principal axes of the hyperbola make an angle f displaystyle varphi nbsp with the positive x displaystyle x nbsp axis that is given bytan 2 f 2 A x y A x x A y y displaystyle tan 2 varphi frac 2A xy A xx A yy nbsp Rotating the coordinate axes so that the x displaystyle x nbsp axis is aligned with the transverse axis brings the equation into its canonical formx 2 a 2 y 2 b 2 1 displaystyle frac x 2 a 2 frac y 2 b 2 1 nbsp The major and minor semiaxes a displaystyle a nbsp and b displaystyle b nbsp are defined by the equationsa 2 D l 1 D D l 1 2 l 2 b 2 D l 2 D D l 1 l 2 2 displaystyle begin aligned a 2 amp frac Delta lambda 1 D frac Delta lambda 1 2 lambda 2 1ex b 2 amp frac Delta lambda 2 D frac Delta lambda 1 lambda 2 2 end aligned nbsp where l 1 displaystyle lambda 1 nbsp and l 2 displaystyle lambda 2 nbsp are the roots of the quadratic equation div, wikipedia, wiki, book, books, library,