z=3x-2y
代入x+y+z=7
x+y+3x-2y=7
4x-y=7 (1)
x+2y=4 (2)
(1)×2+(2)
8x+x=14+4
9x=18
所以
x=2
y=4x-7=1
z=3x-2y=4
{ x+y+z=7 x+2y=4 z=3x-2y 解方程组
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