为了方便书写，我令x=sin(alpha)，y=cos(alpha)
另外几条你应该已经了解的公式
x^2+y^2=1
sin(2alpha)=2xy
cos(2alpha)=1-2x^2
下面开始推导
[2xy/(1-(1-2x^2))]*[y/(1-x)]
=[2xy/2x^2]*[y/(1-x)]
=[y/x]*[y/(1-x)]
=y^2/[x(1-x)]
=(1-x^2)/[x(1-x)]
=[(1+x)(1-x)]/[x(1-x)]
=(1+x)/x
另外几条你应该已经了解的公式
x^2+y^2=1
sin(2alpha)=2xy
cos(2alpha)=1-2x^2
下面开始推导
[2xy/(1-(1-2x^2))]*[y/(1-x)]
=[2xy/2x^2]*[y/(1-x)]
=[y/x]*[y/(1-x)]
=y^2/[x(1-x)]
=(1-x^2)/[x(1-x)]
=[(1+x)(1-x)]/[x(1-x)]
=(1+x)/x
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2楼2015-03-23 15:23
2楼2015-03-23 15:23收起回复
