f*x(=1/2*sin4x-√3(1-cos4x)/2
=sin4xcosπ/3+cos4xsinπ/3-√3/2
=sin(4x+π/3)-√3/2
π/3<=4x+π/3<=4π/3
所以-√3/2<=sin(4x+π/3)<=1
在减去-√3/2
值域[-√3,1-√3/2]