Question

How do you show this? I’m struggling to figure it out

Answer 1

Refer to the attached file.

Just replace cos2x with cos²x-sin²x

and work out.

I hope it helps u

Answer 2

1 + cos(2x) = 1 + 2cos²x - 1 = 2cos²x

1 - cos(2x) = 1 - 1 + 2sin²x = 2sin²x

2cos²x/2sin²x

cot²x

d(cot²x)/dx = 2cotx × -cosec²x

= -2cotx cosec²x