sinA/(1-cotA)+cosA/(1-tanA)
=sinA/[1-(cosA/sinA)]+cosA/[1-sinA/cosA]
=(sinA)^2/[sinA-cosA]+(cosA)^2/[cosA-sinA]
=[(cosA)^2-(sinA)^2]/[cosA-sinA]
=cosA+sinA
=√2[(√2/2)cosA+(√2/2)sinA]
=√2sin(45°+A)
用到的三角公式有:cotA=cosA/sinA tanA=sinA/cosA sin(A+B)=sinAcosB+cosAsinB