cosα*根号[（1-sinα）/（1+sinα）]+sinα*根号[（1-cosα）/（1+cosα）] =cosα*根号[(1-sinα)^2/(1-sin^2α)]+sinα*根号[(1-cosα)^2/(1-cos^2α)] =cosα*(1-sinα)/cosα+sinα*(1-cosα)/sinα =(1-sinα)+(1-cosα) =2-sinα-cosα
