已知sinα=3/5,α∈（0，π/2),cosβ=4/5,β∈（-π/2,0),那么：cosα=根号(1-sin²α)=4/5，sinβ=-根号(1-cos²β)=-3/5所以：sin(α+β）=sinαcosβ+ cosαsinβ =(3/5)*(4/5) +(4/5)*(-3/5) =0
