How do you use the double angle formula to rewrite 4-8sin^2x?

Answer 1

cos 2x can be written in 3 ways:

cos²x - sin²x

2 cos²x - 1

1 - 2sin²x

The last of these will be used here

4 - 8 sin²x = 4(1 - 2sin²x) = 4 cos 2x