It is proved that: (1-sin2 α) / (Cos2 α) = (1-tan α) / (1 + Tan α)

（1-tanα）/（1+tanα） =(1-sinα/cosα)/(1+sinα/cosα)=((cosα-sinα)/cosα)/((cosα+sinα)/cosα)=(cosα-sinα)/(cosα+sinα)=((cosα-sinα)*(cosα-sinα))/((cosα+sinα)(cosα-sinα))=(cosα*cosα...

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