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As above, for e = 0, the graph is a circle, for 0 < e < 1 the graph is an ellipse, for e = 1 a parabola, and for e > 1 a hyperbola. The polar form of the equation of a conic is often used in dynamics; for instance, determining the orbits of objects revolving about the Sun. [20]
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). All of these non-degenerate conics have, in common, the origin as a vertex (see diagram).
(The parabolas are orthogonal for an analogous reason to confocal ellipses and hyperbolas: parabolas have a reflective property.) Analogous to confocal ellipses and hyperbolas, the plane can be covered by an orthogonal net of parabolas, which can be used for a parabolic coordinate system .
A family of conic sections of varying eccentricity share a focus point and directrix line, including an ellipse (red, e = 1/2), a parabola (green, e = 1), and a hyperbola (blue, e = 2). The conic of eccentricity 0 in this figure is an infinitesimal circle centered at the focus, and the conic of eccentricity ∞ is an infinitesimally separated ...
Then for the ellipse case of AC > (B/2) 2, the ellipse is real if the sign of K equals the sign of (A + C) (that is, the sign of each of A and C), imaginary if they have opposite signs, and a degenerate point ellipse if K = 0. In the hyperbola case of AC < (B/2) 2, the hyperbola is degenerate if and only if K = 0.
If e > 1, this equation defines a hyperbola; if e = 1, it defines a parabola; and if e < 1, it defines an ellipse. The special case e = 0 of the latter results in a circle of the radius ℓ {\displaystyle \ell } .
The latus rectum is defined similarly for the other two conics – the ellipse and the hyperbola. The latus rectum is the line drawn through a focus of a conic section parallel to the directrix and terminated both ways by the curve. For any case, is the radius of the osculating circle at the vertex.
This line meets the circumcircle of ABC in 0,1, or 2 points according as the circumconic is an ellipse, parabola, or hyperbola. The general inconic is tangent to the three sidelines of ABC and is given by the equation + + =