由x+y-2z=5得2x+2y-4z=10
2x+2y-4z=10与2x-y-z=4相减得y-z=2
由x+y-2z=5得3x+3y-6z=15
3x+3y-6z=15与3x+y-3z=10相减得
由2y-2z=4与2y-3z=5得y=1 z=-1
代入原方程组解得x=2
综上x=2 y=1 z=-1