若cos2x=-3/4,那么sin^4+cos^4=
问题描述：
若cos2x=-3/4,那么sin^4+cos^4=
答
cos2x=(cosx)^2 - (sinx)^2 = -3/4
又
(cosx)^2 + (sinx)^2 = 1
则
sin^4+cos^4
=[((cosx)^2 + (sinx)^2 )^2 + ((cosx)^2 - (sinx)^2 )^2] /2
=(1 + 9/16)/2
=25/32