已知cos[a-(b/2)]=-1/9,sin[(a/2)-b]=2/3.且π/2

Question

已知cos[a-(b/2)]=-1/9,sin[(a/2)-b]=2/3.且π/2

Answer 1

设a-(b/2)=α ,(a/2)-b=β
则(a+b)/2=α-β
∴sin(a+b)/2=sin(α-β)=sinαcosβ-cosαsinβ
∵π/2