Question

1+cos(18x)=______
Please answer this

Answer 1

Answer with Explanation:

Keep in mind these trigonometric Identity:

1. Cos²x - Sin² x= Cos 2 x

2. Cos 2 x = 2 Cos²x-1

3. Cos 2 x = 1 - 2 Sin²x

Now, Coming to the Problem

1 + Cos (18 x)

= 1 + Cos (2 × 9 x)

= 2 Cos ² (9 x)→→→ Cos (2 × 9 x)= 2 Cos² (9 x) - 1