cos2x=3/5.sin^4+cos^4x=?

cos2x=3/5.sin^4+cos^4x=?
cos2x=3/5.sin^4+cos^4x=?

cos2x=3/5.sin^4+cos^4x=?
(sinx)^4+(cosx)^4
=[(sinx)^2+(cosx)^2]^2-2(sinx)^2(cosx)^2
=1-(1/2)[sin(2x)]^2
=1-(1/2)[1-cos(2x)^2]
=1-(1/2)[1-(3/5)^2]
=1-8/25
=17/25