Q. If $\sec{\theta = m}$ and $\tan{\theta = n}$, then $\frac{1}{m}\left\lbrack (m + n) + \frac{1}{(m + n)} \right\rbrack$ is

A) 2
B) $2m$
C) $2n$
D) $mn$
Explanation

(a)
$\frac{1}{m}\left\lbrack (m + n) + \frac{1}{(m + n)} \right\rbrack$
$= \frac{1}{\sec\theta}\left\lbrack \sec{\theta + \tan{\theta + \frac{1}{\sec{\theta + \tan\theta}}}} \right\rbrack$
$= \frac{\lbrack\sec^{2}{\theta + \tan^{2}{\theta + 2\sec{\theta\tan{\theta + 1}}}}\rbrack}{\sec{\theta(\sec{\theta + \tan\theta})}}$
$= \frac{2\sec^{2}{\theta + 2\sec{\theta\tan\theta}}}{\sec{\theta(\sec{\theta + \tan\theta})}}$
$= 2$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

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