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^...