原式=6xy-[4xy-(2xyz-2xz)-8xz]-xyz =6xy-(4xy-2xyz+2xz-8xz)-xyz =6xy-4xy+2xyz-2xz+8xz-xyz =2xy+xyz+6xz =x（2y+yz+6z）当x=-2，y=-3，z=1时原式=-2*[2*(-3)+(-3)*1+6*1] =6
