y=sin²x+√3sinxcosx－1
=√3sinxcosx－1+sin²x
=(√3/2)2sinxcosx－1/2+sin²x-1/2
=(√3/2)sin2x－(1-2sin²x)/2-1/2
=(√3/2)sin2x－(cos2x)/2-1/2
=cos(π/6)sin2x－cos2xsin(π/6)-1/2
=sin(2x-π/6)-1/2