Question

Total number of solutions of equation $\sin x.\tan 4x=\cos x$ belonging to $(-\pi ,2\pi )$ are:

• A. 4
• B. 7
• C. 8
• D. 15

Answer 1

Answer: (D)

$\sin x\cdot \tan 4x=\cos x$
$\Rightarrow \sin x\sin 4x=\cos x\cos 4x$
$\Rightarrow \cos 5x=0$
$\Rightarrow$ five solutions.