Question

If cos 2θ = sin 4θ and 2θ and 4θ are acute angles then find θ.

Answer 1

Given :

cos 2θ = sin 4θ

or cos 2θ = cos(90° – 4θ) [∵ cos(90° – θ) = sin θ]

or 2θ = 90° – 4θ

or 6θ = 90°

or θ = 90°/6

θ = 15°