Question

If $\cos ^2 \theta=\cos 2 \theta$, then the general value of $\theta$ is

(A) $n \pi$

(B) $2 n \pi$

(C) $\frac{n \pi}{3}$

(D) $\frac{n \pi}{2}$

Answer 1

SOLUTION — We have,

$\begin{array}{ll}\text {  We have, } & \cos ^2 \theta=\cos 2 \theta \\\Rightarrow & \cos ^2 \theta=2 \cos ^2 \theta-1 \\\Rightarrow & \cos ^2 \theta=1=\cos ^2(0)\end{array}$

$\Rightarrow \quad \theta=n \pi$

So, The correct option will be (A).