sinα=12/13 α∈(0,π/2) cosβ=-3/5.β∈﹙π,3π/2﹚求sin﹙α+β)

问题描述:

sinα=12/13 α∈(0,π/2) cosβ=-3/5.β∈﹙π,3π/2﹚求sin﹙α+β)

sinα=12/13
(sinα)^2+(cosα)^2=1
且α∈(0,π/2)
所以cosα>0
cosα=5/13
cosβ=-3/5
(sinα)^2+(cosα)^2=1
且β∈(π,3π/2)
所以sinβ<0
sinβ=-4/5
sin(α+β)=sinαcosβ+sinβcosα
=-56/65
题是纯手打啊
不懂可以继续追问啊