Question

若有关于x,y的方程组：x+2y=3m,x-y=9m,的解，也是方程3x+2y=17的解，则m的值为？

初一数学题

Answer 1

x+2y=3m (1)
x-y=9m (2)
(1)*5+(2)*4
5x+10y+4x-4y=15m+36m
9x+6y=51m
3x+2y=17m
满足3x+2y=17
所以17m=17
m=1

Answer 2

解： 把 x+2y=3m
减 x-y=9m
x-y-x-2y=6m
y=-2m
将 y=-2m代入 x+2y=3m
得 x=7m
再将 x=7m,y=-2m代入3x+2y=17
得m=1

Answer 3

其实就是解方程组:
x+2y=3m (1)
x-y=9m (2)

(1)-(2)得:
3y=-6m
y=-2m
解方程组得:
x=7m
y=-2m

将x=7m，y=-2m代入3x+2y=17得:
21m-4m=17
17m=17
m=1

Answer 4

x+2y=3m (1)
x-y=9m (2)
(1)*5+(2)*4
5x+10y+4x-4y=15m+36m
9x+6y=51m
3x+2y=17m
满足3x+2y=17
所以17m=17
m=1