a) {7x+10y=3
{2x-5y=7 inmultim -2
{7x+10y=3
{-4x-10y=-14
3x / =-11
x=-11/3
din 2x-5y=7 avem
-22/3-5y=7
-5y=7+22/3
-5y=(21+22)/3
-5y=43/3 inmultim -1
y=-43/(3·5)
y=-43/15
B){2x+7y=6 inmultim cu -3
{6x+21y=18
{-6x-21y=-18
{6x+21y=18
/ / 8
sistemul nu are solutii
x∈Ф si y∈Ф
c) {4x-5y=1 inmultim -2
{8x-10y=-1
{-8x+10y=-2
{8x-10y=-1
/ /
sistemul nu are solutii
x∈Ф si y∈Ф
d) {3x-15y=1
{x+5y=0 inmultim cu 3
{3x-15y=1
{3x+15y=0
6x / =1
x=1/6
din x+5y=0 avem
1/6+5y=0
5y=-1/6
y=-1/(5·6)
y=-1/30