y=sin^4x+2√3 sinxcosx-cos^4x
=(sin^2x+cos^2x)(sin^2x-cos^2x)+√3sin2x
=(sin^2x-cos^2x)+√3sin2x
=-cos2x+√3sin2x
=2(-1/2*cos2x+√3/2*sin2x)
=2sin(2x-π/6)