2x+3y+z=6 (1)x-y+2z=-1 (2)x+2y-z=5 (3)(1)+(3)式得:3x+5y=11 (5)(3)乘2得:2x+4y-2z=10 (4)(4)+(2)得:3x+3y=9 (6)(5)-(6)式得:2y=2y=1把y=1代入(6)得:3x+3=93x=6x=2把x=2,y=1代入(1)得:4+3+z=6z=-1所以解为:x=2y=1z=-1