√(1+sinα)/(1-sinα)-√(1-sinα)/(1+sinα)
=√(1+sinα)^2/(1-sin^2α)-√(1-sinα)^2/(1-sin^2α)
=(1+sinα)/｜cosα｜-(1-sinα)/｜cosα｜
=2sinα/｜cosα｜
=-2tanα
α属于(2kπ+π/2,2kπ+3π/2),k属于Z