已知cos2θ=根号2/3,则 sin^4θ+cos^4θ的值为________.
已经求到(sin^2θ+cos^2θ)^2=1
(sin^2θ+cos^2θ)^2-2sin^2θcos^2θ=1-2sin^2θcos^2θ
人气:362 ℃ 时间:2019-09-23 14:01:44
解答
sin^4a+cos^4a
=(sin²a+cos²a)²-2sin²acos²a
=1-(1/2)sin²2a
=1-(1/2)[1-cos²2a]
=1-(1/2)[1-(2/9)]
=11/18
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