Jawabanmu

2014-06-06T13:14:58+07:00
(sin^4 x - cos^4 x)
= (sin^2 x + cos^2 x)(sin^2 x - cos^2 x)
= (sin^2 x - cos^2 x)
= sin^2 x - 1 + sin^2 x
= 2sin^2 x - 1