a) x+2y=9
y-1 =3x
x+2y=9
y-3x=1
x+2y=9 /* (-3)
-3x+y=1
-3x-6y=-27
-3x+y=1
-5y=-26 / : (-5)
y=5 1/5
y-1=3x
5 1/5 -1=3x
4 1/5=3x
3x=4 1/5 / :3
x= 1,4
b) x-y=2
½x-1=¼y
x-y=2
1/2x-1/4y=1 /(-2)
x-y=2
-x+1/2y=-2
-1/2y=0 /* 2
y=0
x-y=2
x-0=2
x=2
c) -x -y =2
2(3x+y)=-20
-x-y=2 / * 2
6x+2y=-20
-2x-2y=4
6x+2y=-20
4x=-16 / :4
x=-4
-(-4) - y=2
4-y=2
-y=2-4
-y=-2 /* (-1)
y=2
d) 4x+3y =54
⅓x= 4( 1+⅛y)
4x+3y=54
1/3x=4+1/2y
4x+3y=54
1/3x-1/2y=4 /*6
4x+3y=54
2x-3y=24
6x=78 /:6
x=13
4*13+3y=54
52+3y=54
3y=54-52
3y=2 /:3
y=2/3
Myślę, że dobrze;)
