x+2y+z=0 x-y+2z=2 2x-y+3z=-1x+2y+z=0 ①x-y+2z=2 ②2x-y+3z=-1 ③①-②得 3y-z=-2④2*①-③得 5y-z=1⑤5*④-3*⑤得 -2z=-13,z=13/2代入z到④,得y=3/2代入y和z到①,得x=-19/2因此 x=-19/2 ...