Question

a (ii) If A=30.verify that cos 2A = 2 cos? A-1 = 1-2 sinA ​

Answer 1

Answer:

Given :-

⋆ A = 30°

To find :-

(a) Cos 2A = Cos 2(30°)

= Cos 60°

= 1/2 (1)

2Cos² A - 1 = 2Cos²30° - 1

= 2(√3/2)² - 1

= 2(3/4) - 1

= 3/2 - 1

= 1/2 (2)

1 - 2sin²A = 1 - 2 Sin²30°

= 1 - 2(1/2)²

= 1 - 1/2

= 1/2 (3)

(1) = (2) = (3),

Cos 2A = 2Cos² A - 1 = 1 - 2sin²A

Hence it proved. ✌