Let $H: \frac{-x^2}{a^2}+\frac{y^2}{b^2}=1$ be the hyperbola, whose eccentricity is $\sqrt{3}$ and the length of the latus rectum is $4 \sqrt{3}$. Suppose the point $(\alpha, 6), \alpha>0$ lies on $H$. If $\beta$ is the product of the focal distances of the point $(\alpha, 6)$, then $\alpha^2+\beta$ is equal to
Solution
<p>$$\begin{aligned}
& H: \frac{x^2}{a^2}-\frac{y^2}{b^2}=-1 \\
& e=\sqrt{1+\frac{a^2}{b^2}}=\sqrt{3} \\
& \Rightarrow 1+\frac{a^2}{b^2}=3 \\
& \Rightarrow \frac{a^2}{b^2}=2 \quad \text{.... (1)}\\
& \frac{2 a^2}{b}=4 \sqrt{3}
\end{aligned}$$</p>
<p>Using equation (1)</p>
<p>$$\begin{aligned}
& \frac{4 b^2}{b}=4 \sqrt{3} \\
& \Rightarrow b=\sqrt{3} \\
& a=\sqrt{6} \\
& H: \frac{x^2}{6}-\frac{y^2}{3}=-1 \\
& \frac{\alpha^2}{6}-12=-1 \\
& \frac{\alpha^2}{6}=11 \\
& \begin{array}{c}
\alpha^2=66 \\
\text { Focus }:(0, b c)(0,-b c) \\
(0,3),(0,-3)
\end{array} \\
& \beta=\sqrt{\alpha^2+9} \times \sqrt{\alpha^2+81} \\
& \beta=105 \\
& \alpha^2+\beta=66+105 \\
& =171
\end{aligned}$$</p>
About this question
Subject: Mathematics · Chapter: Conic Sections · Topic: Parabola
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