Question

{x-2y=12
{x-2y=12 

Answer 1

-4y=24
-y=24/4
-y=6
y=-6

x-2*(-6)=12
x-(-12)=12
x+12=12
x=12-12
x=0

Answer 2

$\left \{ {{x-2y=12} \atop {x+2y=12}} \right.$
x-2y=12
x=12+2y
x+2y=12
12+2y+2y=12
2y+2y=12-12
4y=0
y=$\frac{0}{4}$
y=0
x-2y=12
x-0=12
x=12-0
x=12
S{0,12}