(cos2x-sin2x)/[(1-cos2x)(1-tan2x)] =cos2x/(1-cos2x)=[cosx)^2-(sinx)^2]/2(sinx)^2 这步是怎么换算的?
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![(cos2x-sin2x)/[(1-cos2x)(1-tan2x)] =cos2x/(1-cos2x)=[cosx)^2-(sinx)^2]/2(sinx)^2 这步是怎么换算的?](/uploads/image/z/2524324-4-4.jpg?t=%28cos2x-sin2x%29%2F%5B%281-cos2x%29%281-tan2x%29%5D+%3Dcos2x%2F%281-cos2x%29%3D%5Bcosx%29%5E2-%28sinx%29%5E2%5D%2F2%28sinx%29%5E2+%E8%BF%99%E6%AD%A5%E6%98%AF%E6%80%8E%E4%B9%88%E6%8D%A2%E7%AE%97%E7%9A%84%3F)
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(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)