Question

cos^4-sen^4+1=2 cos^2

Answer 1

sen^4(x) - cos^4(x) =

(sen^2(x) - cos^2(x) )(sen^2(x) + cos^2(x)) =

(sen^2(x) - cos^2(x) )(1) =

1 - cos^2(x) - cos^2(x)

1 - 2cos^2(x)