Question

trigonometric identities:
cos^4a-sen^4a+1=2cos^2a

Answer 1

You mean sin

Here's a hint. Write c = cos a, and s = sin a.

Then c^4 - s^4
= (c^2 - s^2)(c^2 + s^2)
= c^2 - s^2

Answer 2

thanks, but i already had that part :S i needed the rest, im on c^2-s^2=2c^2