Question

can someone please help me prove the identity:
cos^4 x- sin^4 x =cos^2 x- sin^2 x

Answer 1

well factor the left side

\[(\cos^2(x) - \sin^2(x))(\cos^2(x) + \sin^2(x)) = (\cos^2(x) - \sin^2(x)) \]

and you know

\[\cos^2(x) + \sin^2(x) = 1\]

so you should be able to prove it from here

Answer 2

now i'm embarrassed, i totally forgot about factoring, thank you