Question

Find θ if 0° < θ ≤ 90°.

cos θ = 2 cos² 30° − 1

Answer 1

Given:

0° < θ ≤ 90°

cos θ = 2 cos² 30° − 1

= cos(2 × 30°)

= cos 60°

= `1/2`   ...[Since 0° < θ ≤ 90°, cos θ = `1/2` gives]

= θ = 60°