α第二象限角
sinα＞0,cosα＜0
cosα * 根號[(1-sinα)/(1+sinα)] + sinα *根號〔(1-cosα)/(1+cosα)〕
=cosα * 根號[(1-sinα)^2/(1-sin^2α)] + sinα *根號〔(1-cosα)^2/(1-cos^2α)〕
=cosα * 根號[(1-sinα)^2/cos^2α] + sinα *根號〔(1-cosα)^2/sin^2α〕
=cosα * (1-sinα)/(-cosα) + sinα *(1-cosα)/sinα
=- (1-sinα) + (1-cosα)
=sinα-cosα