Gujarati
10-2. Parabola, Ellipse, Hyperbola
medium

The equation of an ellipse whose eccentricity is $1/2$ and the vertices are $(4, 0)$ and $(10, 0)$ is

A

$3{x^2} + 4{y^2} - 42x + 120 = 0$

B

$3{x^2} + 4{y^2} + 42x + 120 = 0$

C

$3{x^2} + 4{y^2} + 42x - 120 = 0$

D

$3{x^2} + 4{y^2} - 42x - 120 = 0$

Solution

(a) Major axis $ = 6 = 2a$ $⇒$ $a = 3$

$e = \frac{1}{2}$ $⇒$ $b = 3\sqrt {1 – \frac{1}{4}} = \frac{{3\sqrt 3 }}{2}$.

Also centre is $(7, 0)$

Equation is $\frac{{{{(x – 7)}^2}}}{9} + \frac{{{y^2}}}{{(27/4)}} = 1$

$3{x^2} + 4{y^2} – 42x + 120 = 0$.

Standard 11
Mathematics

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