二元一次解方程高手請進

2X+Y=7------(1)
3X-Y=8------(2)
(1)+(2)
2X+3X=7+8
5X=15
X=3
3(3)-Y=8
Y=9-8
Y=1

2X+5Y=7------(1)
2X+Y=5------(2)
(1)-(2)
5Y-Y=7-5
4Y=2
Y=1/2
2X+1/2=5
X=(9/2)/2
X=9/4


5X+3Y=10------(1)
X+2Y=9------(2)
(2)x5-(1)
10Y-3Y=45-10
7Y=35
Y=5
X+2(5)=9
X=9-10
X=-1

2X+Y=7------(1)
3X-Y=8------(2)

(1)+(2):
2X+3X+Y-Y=7+8
5X =15
X =3

把X=3代入(1)
2(3)+Y=7
Y=7-6
Y=1



2X+5Y=7------(1)
2X+Y=5------(2)

(1)-(2):
2X-2X+5Y-Y=7-5
4Y=2
Y=1/2

把Y=1/2代入(2)
2X+1/2=5
X=9/4



5X+3Y=10------(1)
X+2Y=9------(2)

(2)x5:
5X+10Y=45------(3)

(3)-(1):
5X-5X+10Y-3Y=45-10
7Y=35
Y=5

把Y=5代入(2)
X+2(5)=9
X+10=9
X=-1