19过程和结果 

解x,y的值
5x+2y=11a+18 ①
2x-3y=12a-8 ②
①×3得 15x+6y=33a+54 ③
②×2得 4x-6y=24a-16 ④
③+④得 19x=57a+38
x=3a+2 ⑤
⑤代入①得 5(3a+2)+2y=11a+18
15a+10+2y=11a+18
2y=11a+18-15a-10
2y=8-4a
y=4-2a
解得 x=3a+2 y=4-2a
a的取值范围
3a+2>0
3a>-2
a>-2/3
4-2a>0
-2a>-4
a