Y=cos(2a-π/3）+sin(a-π/4)sin(a+π/4)= cos(2a-π/3）+ sin(a-π/4)sin[(a-π/4)+π/2]= cos(2a-π/3）+ sin(a-π/4)cos(a-π/4)= cos(2a-π/3）+1/2*sin(2a-π/2)= cos(2a-π/3）-1/2*cos(2a)= cos(2a) cosπ/3+...