sin(540°+α)cos(360°-α)/sin(450°+α)tan(900°-α)

题目

sin(540°+α)cos(360°-α)/sin(450°+α)tan(900°-α)
急!

答案

sin(540°+α)cos(360°-α)/[sin(450°+α)tan(900°-α)]
=sin(180°+α)cosα/[sin(90°+α)tan(180°-α)]
=-sinαcosα/[-cosα.tanα]
=-sinαcosα/[-sinα]
=cosα