当cosα=0时,原式=sinα/sinα=1当cosα≠0时,分子分母除以cosα得原式=(tanα+1)/(tanα-1)360°=2π1°=π/180180°/π=1弧度单位省略
原式=(1+tanα)/(1-tanα)=(tan45°+tanα)/(1-tan45°tanα)=tan(45°+α)
