sinα=-2根号5/5
cosα=-根号5/5
tanβ=1/3
sinβ=根号10/10
cosβ=3根号10/10
sin(α-β)=sinαcosβ-cosαsinβ
=-6根号50/50+根号50/50
=-5根号50/50
=-根号2/2
α-β=5π/4