Question

if cos2θ=cos²θ then θ=

Answer 1

$\cos(2 \theta) = { \cos}^{2} \theta \\ 2{ \cos}^{2} \theta - 1 ={ \cos}^{2} \theta \\ { \cos}^{2} \theta = 1 \\ \cos\theta = + 1 \: \: or \: \: - 1 \\ \theta = 0 \: \: or \: \: \pi$