Q. If the line $3x-2y+12=0$ intersects the parabola $4y=3x^2$ at the points $A$ and $B$, then at the vertex of the parabola, the line segment $AB$ subtends an angle equal to

A) $\tan^{-1}\left(\frac45\right)$
B) $\tan^{-1}\left(\frac97\right)$
C) $\tan^{-1}\left(\frac{11}9\right)$
D) $\frac\pi2-\tan^{-1}\left(\frac32\right)$
Explanation

[Solution by Dr. Abubacker] Substituting $y=\frac{3x+12}2$ into $4y=3x^2$: $x^2-2x-8=0$, so $A(4,12)$ and $B(-2,3)$. The vertex is $O(0,0)$: $\vec{OA}=(4,12)$, $\vec{OB}=(-2,3)$. $\tan\theta=\frac{|4\cdot3-12\cdot(-2)|}{4(-2)+12\cdot3}=\frac{36}{28}=\frac97$. Answer (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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