Question

Find the angle θ, when 0° < θ < 90°.

cos θ = cos² 30° − sin² 30°

Answer 1

cos θ = cos² 30° − sin² 30°, 0° < θ < 90°

cos² − sin² = cos²

cos² 30° − sin² 30° = cos(2 × 30°) = cos 60°

cos θ = cos 60°

cos 60° = `1/2`

cos θ = `1/2`

θ = 60°