Răspuns:
a){4*x-y=-1
{x+y=4
{4*x-y=-1
{y=4-x
4*x-(4-x)=-1
x=3/5
y=4-3/5
y=17/5
{x,y}={3/5;17/5}
b){x-y=-5
{3*x+2*y=19
{x=-5+y
{3*x+2*y=19
3*(-5+y)+2*y=19
y=34/5
x=-5+34/5
x=9/5
{x,y}={9/5;34/5}
c)2*x+y=13
3*x+y=6
y=13-2*x
3*x+y=6
3*x+13-2*x=6
x=-7
y=13-2*(-7)
y=27
{x,y}={-7;27}
d){1-x+3y = 19
{1x + 5y = 15
{1-x+3*y=19
{x=15-5*y
1-(15-5*y)+3*y=19
y=33/8
x=15-5*33/8
x=-45/8
{x,y}={-45/8;33/8}