cosα=-√5/5 ,sinα==-2√5/5,tanβ=1/3sinβ=3cosβ ,1-cos^2β=9cos^2βcosβ=√10/10,sinβ=3√10/10 sin(α-β)=sinαcosβ-cosαsinβ=-2√5/5*√10/10-(-√5/5)*3√10/10 =(15√2-10√2)/50=√2/10α-β=0.00...