3x^2y-{xyz-（2xyz-x^2z）-4x^2z+[3x^2y-(4xyz-5x^2z-3xyz)]}
=3x^2y-[xyz-2xyz+x^2z-4x^2z+(3x^2y-4xyz+5x^2z+3xyz)]
=3x^2y-(xyz-2xyz+x^2z-4x^2z+3x^2y-4xyz+5x^2z+3xyz)
=3x^2y-xyz+2xyz-x^2z+4x^2z-3x^2y+4xyz-5x^2z-3xyz
=(3-3)x^2y+(-1+2+4-3)xyz+(-1+4-5)x^2z
=2xyz-2x^2z
=2xz(y-x)