Q. The intersection point of the normals drawn at the end points of latusrectum of the parabola $x^{2} = - 2y$ is

A) $\left( - \frac{1}{2}, - \frac{3}{2} \right)$
B) $\left( \frac{1}{2}, - \frac{3}{2} \right)$
C) $(0,1)$
D) $\left( 0, - \frac{3}{2} \right)$
Explanation

(d)
Given parabola is $x^{2} = - 2y$
Coordinates of end points of a latusrectum are $A\left( 1,\ - \frac{1}{2} \right)$ and $B\left( - 1,\ - \frac{1}{2} \right)$
Now, $2x = - 2\frac{dy}{dx}$
$\Rightarrow \frac{dy}{dx} = - x$
And slope of normal is $- \frac{dx}{dy} = \frac{1}{x}$
The equations of normals at points $A$ and $B$ are
$y + \frac{1}{2} = \frac{1}{1}(x - 1)$
$\Rightarrow 2y - 2x = - 3$ …(i)
And $y + \frac{1}{2} = - \frac{1}{1}(x + 1)$
$\Rightarrow 2y + 2x = - 3$ …(ii)
On solving Eqs. (i) and (ii), we get
$x = 0,\ y = - \frac{3}{2}$

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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