{x² +y²=25/4
{xy=3
{x² +y²+2xy-2xy=25/4
{xy=3
{(x +y)²-6=25/4
{xy=3
{(x +y)²=25/4 +6
{xy=3
{(x +y)²=49/4
{xy=3
1.
x+y=7/2
xy=3
y=7/2-x
x(7/2-x)=3
7x/2-x²=3
7x-2x²=6
2x²-7x+6=0
2x²-3x-4x+6=0
x(2x-3)-2(2x-3)=0
(2x-3)(x-2)=0
x=3/2 y=3:(3/2)=2
x=2 y=3/2
2.
x+y=-7/2
xy=3
y=-7/2-x
x(-7/2-x)=3
-7x/2-x²=3
-7x-2x²=6
2x²+7x+6=0
2x²+3x+4x+6=0
x(2x+3)+2(2x+3)=0
(2x+3)(x+2)=0
x=-3/2 y=3:(-3/2)=-2
x=-2 y=-3/2