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10-2. Parabola, Ellipse, Hyperbola
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If area of quadrilateral formed by tangents drawn at ends of latus rectum of hyperbola $\frac{x^2}{a^2}-\frac{y^2}{b^2}=1$ is equal to square of distance between centre and one focus of hyperbola, then $e^3$ is ($e$ is eccentricity of hyperbola)
A
$2\sqrt 2$
B
$2$
C
$3$
D
$8$
Solution
ends of $L.R$ $\left(\pm a e, \pm \frac{b^{2}}{a}\right)$
$\Rightarrow$ tan gents are $\pm \frac{\mathrm{e}}{\mathrm{a}} \mathrm{x} \pm \frac{1}{\mathrm{a}} \mathrm{y}=1$
$\Rightarrow$ Area $=\frac{2 a^{2}}{e}-a^{2} e^{2}$
$\Rightarrow \mathrm{e}^{3}=2$
Standard 11
Mathematics
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