5x-4y=9
3x+2y=1
din a doua
y=(1-3x)/2
5x+4.(1-3x)/2=9
5x+2-6x=9
-x=7 ⇒x=-7
{5x-4y=9
{3x+2y=1
x=(1-2y)/3
5.(1-2y)/3-4y=9
5-10y-12y=27
-22y=22
{y=-1
{x=-7
b)6x-7y=18
2x+5y=6
x=(18+7y)/6
2.(18+7y)/6 +5y=6
18+7y+15y=18
22y=0
y=0
si
y=(6x-18)/7
2x+5.(6x-18)/7=6
14x+30x-90=42
44x=132
{x=3
{y=0
