解方程组1.2x+y+z=7 2.x+2y+z=5 3.x+y+2z=4

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解方程组1.2x+y+z=72.x+2y+z=53.x+y+2z=4解方程组1.2x+y+z=72.x+2y+z=53.x+y+2z=4解方程组1.2x+y+z=72.x+2y+z=53.x+y+2z

解方程组1.2x+y+z=7 2.x+2y+z=5 3.x+y+2z=4
解方程组1.2x+y+z=7 2.x+2y+z=5 3.x+y+2z=4

解方程组1.2x+y+z=7 2.x+2y+z=5 3.x+y+2z=4
x=5-2y-z
2*(5-2y-z)+z=7
5-2y-z+y+2z=4

2x+y+z=7 ①
x+2y+z=5 ②
x+y+2z=4 ③
(①+②+③)/4
x+y+z=4 ④
①-④ :x=3
②-④ : y=1
③-④ z=0

x=3,y=1,z=0

x=3 y=1 z=o

三式相加 x+y+z=4
所以
x=3
y=1
z=0

1+2+3,得4(x+y+z)=16,即x+y+z=4(4式),1、2、3式分别减4式得:x=3,y=1,z=0

2x+y+z=7 ①
x+2y+z=5 ②
x+y+2z=4 ③
②—③: y—z=1 ④
②x2—①:3y+z=3 ⑤
④+⑤: 4y=4
得:y=1
代入④得:z=0
代入②得:x=3

你出错了 1.2x+y+z=7 2.x+2y+z是等式吗?
除非xyz都是0