Question

Find the value of $\theta$ in degrees for $2\cos 3\theta =1$ if $3\theta$ is acute.

Answer 1

$2\cos 3\theta =1$

$\cos 3\theta =\frac{1}{2}\Rightarrow \cos 3\theta =\cos {60}^0\Rightarrow 3\theta ={60}^0\Rightarrow \theta =\frac{{60}^0}{3}={20}^o$