已知x、y、z满足{3x+7y+z=5 ,求x+y+z的值 {4x+10y+z=3

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已知x、y、z满足{3x+7y+z=5 ,求x+y+z的值 {4x+10y+z=3
已知x、y、z满足{3x+7y+z=5 ,求x+y+z的值 {4x+10y+z=3

已知x、y、z满足{3x+7y+z=5 ,求x+y+z的值 {4x+10y+z=3
3x+7y+z=5.(1)
4x+10y+z=3.(2)
(1)*3-(2)*2有
9x+21y+3z-(8x+20y+2z)=5*3-3*2
x+y+z=15-6
x+y+z=9

﹛3x+7y+z=5 ①
﹛4x+10y+z=3 ②
①×3,得9x+21y+3z=15 ③
②×2,得8x+20y+2z=6 ④
③-④,得x+y+z=9.
∴x+y+z的值为9.

3x+7y+z=5 (1)
4x+10y+z=3 (2)
(2)-(1) x+3y=-2 (3)
(1)-2(3) x+y+z=9

3x+7y+z=5 (1)
4x+10y+z=3 (2)
(2)-(1) x+3y=-2 (3)
(1)-2(3) x+y+z=9