已知方程组2x+5y+4z=1 2x+3y-3=0 则式子x+y-z的值为

问题描述:

已知方程组2x+5y+4z=1 2x+3y-3=0 则式子x+y-z的值为

2x+5y+4z=1
2x+3y-3=0
2x+3y=3...............1
2x+5y+4z=1
2x+3y+2y+4z=1
3+2y+4z=1
y+2z=-1.............2
1式-2式得
2x+2y-2z=4
x+y-z=2

2x+5y+4z=1 (1)
2x+3y-3=0 (1)
(2)*3-(1)
6x+9y-9-2x-5y-4z=0-1
4x+4y-4z=8
x+y-z=2