已知3x+7y+z=6.3,4x+10y+z=8.4,那么x+y+z的值为?

已知3x+7y+z=6.3,4x+10y+z=8.4,那么x+y+z的值为?
已知3x+7y+z=6.3,4x+10y+z=8.4,那么x+y+z的值为?

已知3x+7y+z=6.3,4x+10y+z=8.4,那么x+y+z的值为?
3x+7y+z=6.3 ...①
4x+10y+z=8.4 ...②
② - ①得x+3y= 2.1,即x= 2.1-3y .③
将③带入①得6.3-9y+7y+z=6.3,即z=2y
x+y+z= 2.1-3y+y+2y=2.1

这么简单的问题,你肯定没好好学习.值为:2.1\7
两式相减得到X=2.1一3y然后把它代入上面任意一个式中得到Z=2y,然后是X+y+z=2.1一3y+y+2y=2.1

3x+7y+z=6.3(1)
4x+10y+z=8.4(2)
(2)-(1）可得x+3y=2.1则x=2.1-3y
由（1）知Z=6.3-7y-3x则z=2y
x+y+z=2.1-3y+2y+y=2.1

3x+7y+z=6.3 (1)
4x+10y+z=8.4 (2)
(2)-(1)得：x+3y=2.1 (3)
(1)-2*(3)得：x+y+z=2.1