已知sinθ=(2/3)根号2,cos2θ=?

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已知sinθ=(2/3)根号2,cos2θ=?已知sinθ=(2/3)根号2,cos2θ=?已知sinθ=(2/3)根号2,cos2θ=?sin^4a+cos^4a=(sin²a+cos&#

已知sinθ=(2/3)根号2,cos2θ=?
已知sinθ=(2/3)根号2,cos2θ=?

已知sinθ=(2/3)根号2,cos2θ=?
sin^4a+cos^4a
=(sin²a+cos²a)²-2sin²acos²a
=1-(1/2)sin²2a
=1-(1/2)[1-cos²2a]
=11/18