中三數,三條!

1:
x+y+2=5
x=5-2-y
x=3-y

9x-2y=5
9(3-y)-2y=5
27-9y-2y=5
-7y=5-27
y=-22/-7
y=22/7

x=3-y
x=3-22/7
x=-1/7

2:
2x-5y=7
2x=7+5y
x=(7+5y)/2

4x+3y=1
4(7+5y)/2+3y=1
14+10y+3y=1
13y=1-14
13y=-13
y=-1

x=(7+5y)/2
x=(7-5)/2
x=1

3:
x+y=2
x=2-y

x/2-y/3=1
(3x-2y)/6=1
3x-2y=6
3(2-y)-2y=6
6-3y-2y=6
y=0

x=2-y
x=2