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Revision Notes on Ellipse
The foci of the ellipse are S(ae, 0) and S’ = (-ae, 0)
Equations of the directrices are given by x = a/e and x = -a/e
The coordinates of vertices are A’ = (-a, 0) and A = (a,0)
The lengths of the major and minor axis are 2a and 2b respectively.
The length of latus rectum is 2b2/a = 2a(1-e2)
The sum of the focal distances of any pint on the ellipse is equal to the major axis. As a result, the distance of focus from the extremity of a minor axis is equal to semi major axis.
If a question does not mention the relation between a and b then by convention a is assumed to be greater than b i.e. a > b.
The point P(x1, y1) lies outside, inside or on the ellipse according as x12/a2 + y12/b2 – 1>< or = 0.
In parametric form, the equations x = a cos θ and y = b sin θ together represent the ellipse.
The line y = mx + c meets the ellipse x2/a2 + y2/b2 = 1 in either two real, coincident or imaginary points according to whether c2 is < = or > a2m2 + b2
The equation y = mx + c is a tangent to the ellipse if c2 = a2m2+ b2
The equation of the chord of ellipse that joins two points with eccentric angles α and β is given byx/acos (α + β)/2 + y/b sin (α + β)/2 = cos (α - β)/2
The equation of tangent to the ellipse at the point (x1, y1) is given byxx1/a2 + yy1/b2 = 1
In parametric form, (xcosθ) /a + (ysinθ/b) is the tangent to the ellipse at the point (a cos θ a, b sin θ)
Equation of normal
Equation of normal at the point (x1,y1) is
a2x/x1 – b2y/y1 = a2- b
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Solved Examples on Ellipse Illustration 1:...