α,β均为锐角
则
0<α<π/2
0<β<π/2
可知
cosα>0
sin(α+β)>0
cosα=√[1-(sinα)^2]=1/7
sin(α+β)=√[1-(cos(α+β))^2]=5√3/14
sinβ
=sin(α+β-α)
=sin(α+β)cosα-cos(α+β)sinα
=(5√3/14)*(1/7)-(-11/14)*(4√3/7)
=√3/2
β=π/3