1) x^2+2xy=3

x-y=7

2) 2x-3=y

2y+x=-1

3) 3x-5y=6

2x+3y=7

1) x=7+y

(7+y) ^2+2 (7+y) y=3

49+14y+y^2+14y+2y^2=3

3y^2+28y+46=0

D=232

y = (-28+-2sqrt (58)) / 6

x1=7 + (-28+2sqrt (58)) / 6

x2=7 + (-28-2sqrt (58)) / 6

2) 2 (2x-3) + x=-1

5x=5

x=1

y=2-1=-1

3) x=3,5-1,5y

3 (3,5-1,5y) - 5y=6

10,5-4,5y-5y=6

-9,5y=-4,5

y=45/95=9/19

x=3,5-9/19*15/10=3,5-27/38=53/19