Q. The area of the quadrilateral formed by the tangents at the end points of latus rectum to the ellipse $\frac{x^{2}}{9} + \frac{y^{2}}{5} = 1$is

A) 27/4 sq units
B) 9 sq units
C) 27/2 sq units
D) 27 sq units
Explanation

(d)
Given, $\frac{x^{2}}{9} + \frac{y^{2}}{5} = 1\$
Latusrectum of an ellipse be
$ae = \sqrt{a^{2} - b^{2}} = \sqrt{4} = 2$
[image:11_image88.emf]
By symmetry the quadrilateral is rhombus
$\Rightarrow \ Equation\ of\ tangent\ at\ \left( ae,\frac{b^{2}}{a} \right) = \left( 2,\ \frac{5}{3} \right)$
$ie,\ \frac{2}{9}\ x + \frac{5}{3}.\frac{y}{5} = 1$
$\Rightarrow \ \frac{x}{9/2} + \frac{y}{3} = 1$
$\therefore Area\ of\ quadrilateral\ ABCD = 4(area\ of\ \mathrm{\Delta}\ AOB\ )$
$= 4.\left\{ \frac{1}{2}.\frac{9}{2}.3 \right\}$
$= 27\$sq units

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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