怎样将tan(π/4-α)化为cos(π/4+α)/sin(π/4+α)?

题目

怎样将tan(π/4-α)化为cos(π/4+α)/sin(π/4+α)?
练习册上写的步骤.没看懂...

答案

tan(π/4-α)
=tan(π/2-(π/4+α))
=cot(π/4+α)
=cos(π/4+α)/sin(π/4+α)