若sin(π/4-α)=3/5 sin(π/4+β)=12/13
问题描述：
若sin(π/4-α)=3/5 sin(π/4+β)=12/13
0
答
sin(3π/4+β-π/4+α)=sin(π/2+α+β)=-cos(α+β)
cos(3π/4+β)=-12/13
cos(π/4-α)=3/5
sin(3π/4+β-π/4+α)
=cos(π/4-α)sin(3π/4+β)-sin(π/4-α)cos(3π/4+β)
=(5/13)*(3/5)-(-4/5)*(-12/13)
=-33/65