Question

Find the angle θ in the following, if 0° < θ < 90°.

cos 2θ = sin θ

Answer 1

sin θ = cos (90° − θ)

Given:

cos 2θ = sin θ

Replace sin⁡ θ with cos⁡ (90° − θ):

cos 2θ = cos (90° − θ)

For 0° < θ < 90°, we equate angles:

2θ = 90∘ − θ

3θ = 90∘

θ = 30∘