JEE MAIN - Mathematics (2025 - 29th January Morning Shift - No. 5)

Let the ellipse $E_1: \frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$, $a > b$ and $E_2: \frac{x^2}{A^2} + \frac{y^2}{B^2} = 1$, $A < B$ have same eccentricity $\frac{1}{\sqrt{3}}$. Let the product of their lengths of latus rectums be $\frac{32}{\sqrt{3}}$ and the distance between the foci of $E_1$ be 4. If $E_1$ and $E_2$ meet at A, B, C and D, then the area of the quadrilateral ABCD equals :
$ \frac{24\sqrt{6}}{5} $
$ \frac{18\sqrt{6}}{5} $
$ 6\sqrt{6} $
$ \frac{12\sqrt{6}}{5} $

Explanation

$$\begin{aligned} &\begin{aligned} & 2 \mathrm{ae}=4 \\ & 2 \mathrm{a}\left(\frac{1}{\sqrt{3}}\right)=4 \\ & \Rightarrow \mathrm{a}=2 \sqrt{3} \\ & \Rightarrow 1-\frac{\mathrm{b}^2}{12}=\frac{1}{3} \Rightarrow \mathrm{~b}^2=8 \\ & \text { Now } \frac{2 \mathrm{~b}^2}{\mathrm{a}} \cdot \frac{2 \mathrm{~A}^2}{\mathrm{~B}}=\frac{32}{\sqrt{3}} \Rightarrow 2\left(\frac{8}{2 \sqrt{3}}\right) \frac{2 \mathrm{~A}^2}{\mathrm{~B}}=\frac{32}{\sqrt{3}} \\ & \Rightarrow \mathrm{~A}^2=2 \mathrm{~B} \\ & 1-\frac{\mathrm{A}^2}{\mathrm{~B}^2}=\frac{1}{3} \Rightarrow 1-\frac{2 \mathrm{~B}}{\mathrm{~B}^2}=\frac{1}{3} \Rightarrow \mathrm{~B}=3 \\ & \Rightarrow \mathrm{~A}^2=6 \\ & \frac{\mathrm{x}^2}{12}+\frac{\mathrm{y}^2}{8}=1 \ldots . .(1) \\ & \frac{\mathrm{x}^2}{6}+\frac{\mathrm{y}^2}{9}=1 \ldots . .(2) \end{aligned}\\ &\text { On solving (1) & (2) we get } \end{aligned}$$

$$\begin{aligned} &(x, y) \equiv\left(\frac{\sqrt{6}}{\sqrt{5}}, \frac{6}{\sqrt{5}}\right),\left(\frac{-\sqrt{6}}{\sqrt{5}}, \frac{6}{\sqrt{5}}\right),\left(\frac{\sqrt{6}}{\sqrt{5}}, \frac{-6}{\sqrt{5}}\right),\left(\frac{-\sqrt{6}}{\sqrt{5}}, \frac{-6}{\sqrt{5}}\right)\\ &\text { The four points are vertices of rectangle and its area }=\\ &\frac{24 \sqrt{6}}{5} \end{aligned}$$

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