Question

$\cos A\cos 2A\cos 4A...\cos 2^{n-1}A$ equals

• A. $\frac{\sin 2^{n}A}{2^n\sin A}$
• B. $\frac{2^n\sin 2^{n}A}{\sin A}$
• C. $\frac{2^n\sin A}{\sin 2^{n}A}$
• D. $\frac{\sin A}{2^n\sin 2^{n}A}$

Answer 1

Answer: (A)

It is a standard result.
$\cos A\cos 2A\cos 2^{2}A.....\cos 2^{n-1}A$
$=\frac{\sin 2^{n}A}{2^n\sin A}$