1)cosθ=-3/5 ,θ∈(π/2,π)
所以sinθ=√（1-cosθ^2）=4/5
2)sin(θ+π/3)=sinθcosπ/3+cosθsinπ/3
=4/5*1/2+(-3/5)*√3/2=(4-3√3)/10