f(x)=(m+n)m-1
=m²+nm -1
=sin²x+1+√3sinxcosx+1/2 -1
=(1-cos2x)/2+(√3/2)sin2x +1/2
=(√3/2)sin2x -(1/2)cos2x
=sin(2x-π/6)
即 f(x)=sin(2x-π/6)