1) 2x-y=2
3x+y=8 +
—----------
5x-y+y=2+8
5x=10
x=2
2x-y=2 => 4-y=2 => -y=-2 => y=2
2) 2x+y=-3
x-y=-3 +
—----------
3x-y+y=-6
3x=-6
x=-2
x-y=-3 => -2-y=-3 => y=1
3) x+y=2
3x+3y=-6 /:3
—----------
x+y=2
x+y=-2 -
—----------
x+y-x-y=2-(-2)
0=4 => ecuación contradictoria
4) 2x+y=6
2x+y=-2 -
—----------
2x+y-2x-y=6-(-2)
0=8 => ecuación contradictoria