用分析法证明cosθ^4-sinθ^4=cos2θ

求证cos^4θ-sin^4θ=cos2θ 已知sinθ+cosθ=2sinα,sinθcosθ=(sinβ)^2,求证4(cos2α)^2=(cos2β)^2 2sinθ+cosθ/sinθ-3cosθ=-5,求cos2θ+4sinθ cos2θ=根号2/3,则sin^4θ+cos^4θ= 已知cos2θ=3/5,求sin∧4θ+cos∧4θ 已知cos2θ=3/5,求sin^4θ+cos^4θ的值. 若cos2θ=√2/3,则sinθ^4+cos^4的值为 cos2θ=√2/3,则cos^4-sin^4的值为 sinθ+sin2θ/1+cosθ+cos2θ= 2sinα=sinθ+cosθ,sin²β==sinθcosθ.求证cos2β=2cos2α=2cos 已知sinθ+cosθ=2sinα,sinθ·cosθ=sin²β,求证：2cos2α=cos2β. 三角数列题：sinθ sinα cosθ成等差数列,sinθ sinβ cosθ为等比数列,求证2COS2α=cos2β