Calculate the value of A, if :

cos 3A (2 sin 2A - 1) = 0

cos 3A. (2 sin 2A - 1) = 0

⇒ cos 3A = 0 and 2sin 2A - 1 = 0

⇒ cos 3A = 0 and 2sin 2A = 1

⇒ cos 3A = 0 and sin 2A = $\dfrac{1}{2}$

⇒ cos 3A = cos 90° and sin 2A = sin 30°

So, 3A = 90° and 2A = 30°

⇒ A = $\dfrac{90°}{3} = 30°$ and A = $\dfrac{30°}{2} = 15°$

Hence, A = 30° and 15°.