cos2α=cos^2(α)-sin^2(α)=2cos^2(α)-1=1-2sin^2(α)

2sin2α-cos2α+sinαcosα-6sinα+3cosα=0,求2cos2α+sinαcosα/1+tanα. (2sinα+cosα)/(sinα-3cosα)=-5 求cos2α 2sinα=sinθ+cosθ,sin²β==sinθcosθ.求证cos2β=2cos2α=2cos 已知(2sinα-cosα)/(2cosα+sinα)=1,求sin2α-3sinαcosα+4cos2α的值 已知COS2α=1/4,则COS^4+SIN^4+SIN^2αCOS^2α的值等于 已知sinθ+cosθ=2sinα,sinθcosθ=(sinβ)^2,求证4(cos2α)^2=(cos2β)^2 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 化简(sinα-cosα)^2-1/-cos2α 化简:sin^2αsin^2β+cos^2αcos^2β-1/2cos2αcos2β 化解sin^2αsin^2β+cos^2αcos^2β-1/2cos2αcos2β 化简(sinα)^2*(sinβ)^2+(cosα)^2(cosβ)^2-1/2cos2αcos2β