Let the tangent to the parabola $\mathrm{y}^{2}=12 \mathrm{x}$ at the point $(3, \alpha)$ be perpendicular to the line $2 x+2 y=3$. Then the square of distance of the point $(6,-4)$ from the normal to the hyperbola $\alpha^{2} x^{2}-9 y^{2}=9 \alpha^{2}$ at its point $(\alpha-1, \alpha+2)$ is equal to _________.
Answer (integer)
116
Solution
$\because \mathrm{P}(3, \alpha)$ lies on $\mathrm{y}^2=12 \mathrm{x}$
<br/><br/>$\Rightarrow \alpha= \pm 6$
<br/><br/>$$
\text { But, }\left.\frac{\mathrm{dy}}{\mathrm{dx}}\right|_{(3, \alpha)}=\frac{6}{\alpha}=1 \Rightarrow \alpha=6(\alpha=-6 \text { reject })
$$
<br/><br/>Now, hyperbola $\frac{x^2}{9}-\frac{y^2}{36}=1$, normal at
<br/><br/>$$
\begin{aligned}
& \mathrm{Q}(\alpha-1, \alpha+2) \text { is } \frac{9 \mathrm{x}}{5}+\frac{36 y}{8}=45 \\\\
& \Rightarrow 2 x+5 y-50=0
\end{aligned}
$$
<br/><br/>Now, distance of $(6,-4)$ from $2 x+5 y-50=0$ is equal to
<br/><br/>$$
\begin{aligned}
& \left|\frac{2(6)-5(4)-50}{\sqrt{2^2+5^2}}\right|=\frac{58}{\sqrt{29}} \\\\
& \Rightarrow \text { Squareof distance }=116
\end{aligned}
$$
About this question
Subject: Mathematics · Chapter: Conic Sections · Topic: Parabola
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