cos2θ=根号2/3,则sin^4θ+cos^4θ=

问题描述:

cos2θ=根号2/3,则sin^4θ+cos^4θ=

sin^4a+cos^4a
=(sin²a+cos²a)²-2sin²acos²a
=1-(1/2)sin²2a
=1-(1/2)[1-cos²2a]
=11/18