y=3sinχcosχ－4cos²χ+2(1-cos²χ)
=1.5sin2x-6cos²χ+2
=1.5sin2x-3(1+cos2x)+2
=1.5(sin2x-2cos2x)-1
=(1.5*√5)sin(2x+t)-1
所以：-2√5/3-1