281)ա){ x+y-7=0
{ x2+xy+y2=43
{x+y=7
{x2+xy+y2=43
{(x+y)2=72
{x2+xy+y2=43
{x2+2xy+y2=49
{x2+xy+y2=43
{xy=6
{x+y=7
{(7-y)y=6
{x=7-y
{7y-y2-6=0
{x=7-y
x1=6/y1=6/6=1
x2=6/y2=6/1=6
-y2+7y-6=0
D=49-4*(-1)-(-6)=49-24=25
y1=-7-5/(-2)=6
y2=-7+5/(-2)=1
գ){x+y=3
{x2-y2-4xy+11=0
{x+y=3
{x2+y2-4xy=-11
{x=y-3
{(y-3)2+y2-4y(y-3)=-11
9-6y+y2-12y+4y2=-11
4y2-18y+9+11=0
2y2-9y+10=0
D=81-80=1; √1=1
y1=9-1/4=2
y2=9+1/4=2.5
x1=3-2=1
x2=3-2.5=0.5
283)ա){x+y+z=6
{y+z=3
{z=1
{x+2+1=6
{y=3-z=3-1=2
{z=1
{x=6-2-1=3
{y=2
{z=1