积化和差
f(x)=cos(2x-π/3）+2sin(x-π/4)sin(x+π/4)
=cos(2x-π/3）+2×(-1/2){cos[(x-π/4)+(x+π/4)]-cos[(x-π/4)-(x+π/4)]}
=cos(2x-π/3）-[cos2x-cos(-π/2)]
=cos(2x-π/3）- cos2x
=cos2xcos(π/3)+sin2xsin(π/3) - cos2x
=(1/2)cos2x + (√3/2)sin2x - cos2x
=(√3/2)sin2x - (1/2)cos2x
=sin(2x-π/6)