令sinβ=2/√5,2cosα+sinα=√5（cosα*2/√5+sinα*1/√5)=√5,cosαsinβ+cosβsinα=1,sin(α+β)=1=sin（π/2）,α+β=π/2,α=π/2-β,sinα=sin(π/2-β)=cosβ=1/√5=√5/5,cosα=cos(π/2-β)=sinβ=2/√5=...