3x-y+z=3 (1)2x+y-3z=11 (2)x+y+z=12 (3)(1)+(2),得5x-2z=14z=(5x-14)/2(2)-(3),得x-4z=-1z=(x+1)/4(5x-14)/2=(x+1)/4整理,得9x=29x=29/9z=(x+1)/4=19/18x=29/9 z=19/18代入(3)y=12-x-z=12-29/9-19/18=139/18x=29/9 y=139/18 z=19/18