cos2α=1-2sin^2(α) ,那么cosα=?

sin²α*sin²β+cos²α*cos²β-1/2cos2αcos2β=（1-cos2α）/2*（1-cos2β）/2+（1+cos2α）/2*（1+cos2β）/2-1/2cos2α*cos2β=1/4（1+cos2α*cos2β-cos2α-cos2β）+1/4（1+cos2α*cos2β+cos2α+cos2β）-1/2cos2α*cos2β=1/4+1/ 证明:1-cos2α/sinα=2sinα sinα-cosα=1/2 求cos2α 求证：cos2αcos2β=1/2{cos2（α+β）+cos2(α-β)} 若tan(π-α)=1/3,则cos2α/2sinαcosα+cos2α的值为 ((1+cos2α)/(3sin2α))*((2sin^2(α))/cos2α)的化简 ((1+cos2α)/(3sin2α))*((2sin^2(α))/cos2α)的化简 急 ((1+cos2α)/(3sin2α))*((2sin^2(α))/cos2α)的化简 已知α为锐角,且tanα＝1/2,求(sin2αcos2α-sinα)/(sin2αcos2α) 的值要详细过程那! cosα=2sinα则cos2α= 化简(sinα-cosα)^2-1/-cos2α 2cos2α-1/1-2sinα2 化简 化简(sinα)^2*(sinβ)^2+(cosα)^2(cosβ)^2-1/2cos2αcos2β 化简:sin^2αsin^2β+cos^2αcos^2β-1/2cos2αcos2β 化解sin^2αsin^2β+cos^2αcos^2β-1/2cos2αcos2β 化简：sin²αsin²β+cos²αcos²β-1/2cos2αcos2β 化简 sin²αsin²β+cos²αcos²β-1/2（cos2αcos2β） sin²αsin²β+cos²αcos²β-【(1/2)*cos2αcos2β】