锐角α,β满足sinα=√5/5,cosβ=3√10/10
则：cosα=2√5/5,sinβ=√10/10
sinα>sinβ
则：α>β
cos(α-β)=cosαcosβ+sinαsinβ
=(2√5/5)(3√10/10)+(√5/5)(√10/10)
=30√2/50+5√2/50
=35√2/50
=7√2/10
所以,α-β=arccos(7√2/10)