(cos2x-sin2x)/[(1-cos2x)(1-tan2x)] =cos2x/(1-cos2x)=[cosx)^2-(sinx)^2]/2(sinx)^2 这步是怎么换算的?

(cos2x-sin2x)/[(1-cos2x)(1-tan2x)] =cos2x/(1-cos2x)=[cosx)^2-(sinx)^2]/2(sinx)^2 这步是怎么换算的?
(cos2x-sin2x)/[(1-cos2x)(1-tan2x)] =cos2x/(1-cos2x)=[cosx)^2-(sinx)^2]/2(sinx)^2 这步是怎么换算的?

(cos2x-sin2x)/[(1-cos2x)(1-tan2x)] =cos2x/(1-cos2x)=[cosx)^2-(sinx)^2]/2(sinx)^2 这步是怎么换算的?
(cos2x-sin2x)/[(1-cos2x)(1-tan2x)]
=cos2x[1-(sin2x/cos2x)]/[(1-cos2x)(1-tan2x)] （分母部分提出cos2x）
=cos2x(1-tan2x)/[(1-cos2x)(1-tan2x)]
=cos2x/(1-cos2x) （分子分母约去(1-tan2x)）
=[(cosx)^2-(sinx)^2]/2(sinx)^2
（二倍角公式：cos2x=(cosx)^2-(sinx)^2=1-2(sinx)^2,∴1-cos2x=2(sinx)^2）