Q. If the angle $\theta$ is acute, then the acute angle between $x^{2}\left( \cos\theta - \sin\theta \right) + 2xy\cos{\theta + y^{2}\left( \cos\theta + \sin\theta \right) = 0}$ is

A) $2\ \theta$
B) $\frac{\theta}{3}$
C) $\theta$
D) $\frac{\theta}{2}$
Explanation

(c)
On comparing the given equation with standard equation, we get
$a = \cos\theta - \sin\theta,\ b = \cos\theta + \sin\theta,\ h = \cos\theta$
$\tan\phi = \frac{2\sqrt{\cos^{2}\theta - \left( \cos^{2}\theta - \sin^{2}\theta \right)}}{\cos{\theta - \sin{\theta + \cos{\theta +}\sin\theta}}} = \frac{2\sin\theta}{2\cos\theta}$
$\Rightarrow \tan\phi = \tan\theta \Rightarrow \phi = \theta$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.