a)x-y=2
½x-1=¼y
x=2+y
½*(2+y)=1/4y
x=2+y
1+1/2y=1/4y
x=2+y
1=1/4y-1/2y
x=2+y
1=1/4y-2/4y
x=2+y
1=-1/4y/*(-4)
x=2+y
y=-4
x=2-4
y=-4
x=-2
y=-4
B) x+2y=9
9-y=3x
X=9-2y
9-y=3x
x=9-2y
9-y=3*(9-2y)
x=9-2y
9-y=27-6y
x=9-2y
-y+6y=-9+27
x=9-2y
5y=18
x=9-2y
y=3,6
x=9-2*3,6
y=3,6
x=9-7,2
y=3,6
x=1,8
y=3,6
