2元1次formula

3b)x+3y=6...(1)
2x+y=3...(2)
(1)*2-(2)
5y=9
y=9/5
x=3/5
4a)2x-3y=4
4x-2y=8
(1)*2-(2)
-4y=0
y=0
x=2
4b)2x-6y= -22
3x-2y= -12
(2)*3-(1)
7x=-14
x=-2
y=3
5a) 7x+4y=5
2x+2y=1
(2)*2-(1)
-3x=-3
x=1
y=-1/2
5b) 4x-5y=0
2x+3y=11
(2)*2-(1)
11y=22
y=2
x=2.5
6a) 3x+2y= -4
2x-3y= -7
(1)*2-(2)*3
13y=13
y=1
x=-2
6b) 5x-7y=6
7x-5y=3
(1)*7-(2)*5
-24y=27
y=-9/8
x=-3/8
7a)5x-2y=13
2x-5y=1
(1)*2-(2)*5
21y=21
y=1
x=3
7b) 3x-4y=2
2x+3y=7
(1)*2-(2)*3
-17y=-17
y=1
x=2
8a) 2x-11y+4=0
3x-4y+1=0
(1)*3-(2)*2
-25y=-10
y=2/5
x=1/5
8b)8x-3y+4=0
-5x+7y-2又2分之1 =0
(1)*5+(2)*8
41y=0
y=0
x=-1/2