Question

$\cos 3\theta =\cos 2\theta$ (Find general solution).

Answer 1

$$\begin{array}{c}3\theta =2n\pi \pm 2\theta \left[\cdot .\cdot n\in 1\right]\\ 3\theta =2n\pi +2\theta \\ 3\theta -2\theta =2n\pi \\ \theta =2n\pi \\ or3\theta +2\theta =2n\pi \\ 5\theta =2n\pi \\ \theta =\frac{2}{5}n\pi \end{array}$$