1
a-b=5和5a=2b=15
5a=2b=15 好像是5a+2b=15吧
a=25/7
b=-10/7
2
x+y=30和x/0.5+y/0.2=1400
x+y=30
2x+5y=1400
y=1340/3
x=-1250/3
3
2a+3b=6和3a-2b=﹣2
b=24/13
a=6/13
4
2x+5y=8和3x+2y=5
y=14/11
x=9/11
5
1/2x-3/2y=﹣1和2x+y=3
x-3y=-2 2x+y=3
x=11/5
y=-7/5
6
1/3x+1/2y=2和2（x-y)-1=2y-x
2x+3y=12 3y-2x=-1
y=11/6
x=13/4
好累呀!