x+y+z=0① 4x+2y+z=3② 9x-3y+z=28③,把①*2-②,2x+2y+2z-4x-2y-z=0-3, -2x+z=-3 ④,把 ①*3+③,3x+3y+3z+9x-3y+z=0+28,12x+4z=28,3x+z=7 ⑤,⑤-④,得 3x+z+2x-z=7+3,5x=10,x=2,把x=2带入④,得-4+z=-3,z=1,把x=2,z=1...