7X-3Y=-1(1)
4X-5Y=-17(2)
(1)*5
35x-15y=-5(3)
(2)*3
12x-15y=-51(4)
(3)-(4)
23x=46
x=2
把x=2代入(1)
14-3Y=-1
Y=5
X=2
Y=5
2.
10X+3Y+1=0(1)
4X+5Y+8=0(2)
(1)*5
50X+15Y+5=0(3)
(2)*3
12X+15Y+24=0(4)
(3)-(4)
38X-19=0
X=1/2
把X=1/2代入(1)
5+3Y+1=0
Y=-2
X=1/2
Y=-2
3.
3A=5B(1)
2A-3B=1(2)
(1)*2
6A-10B=0(3)
(2)*3
6A-9B=3(4)
(4)-(3)
B=3
把B=3代入(1)
3A=15
A=5
A=5
B=3