Asked by Kiely

cos^4 x - sin^4 x = 1 - 2sin^2 x

Prove
Answered by Michael
Work with only one side to get it to match the other. It's critical you alter only ONE side.

What progress have you made, and where are you having problems?
Answered by Kiely
I am completely stumped. I've never worked with ^4 before and I don't know how to factor it out.
Answered by Michael
Break cos^4(x) into cos^2(x)*cos^2(x).