∵α属于（0,π/2）,且cosα=3/5
∴sinα>0
即sinα=√(1-cos²α)=4/5
则sin(α+π/4)
=sinαcosπ/4+cosαsinπ/4
=4/5*(√2/2)+3/5*(√2/2)
=2√2/5+3√2/10
=7√2/10