a) {x-3y=4 inmultim -5
{5x-2y=-1
{-5x+15y=-20
{5x-2y=-1
-5x+5x+15y-2y=-20-1
13y=-21
y=-21/13
x=4+3y=4-3·21/13=4-63/13=(16-63)/13=-47/13
x=-47/13
prob.b
{3x-y=-2
{0,5x-1+y=8
{3x-y=-2
{0,5x+y=9
3,5x=7
x=7/3,5
x=2
din 3x-y=-2
avem 3·2-y=-2
-y=-2+6
-y=4 inmultim -1
y=-4
