Jawabanmu

2014-05-30T10:41:44+07:00
Sifat cos2x = cos^2 x - sin^2 x = 2cos^2 x - 1=
1 - 2sin^2 x.

cos4x = 1 - 2sin^2 2x

cos4x - 1 = 1 - 2sin^2 2x -1 = -2sin^2 2x