1) x^2+y^2=74

x-y=2

2) x^2+4y^2=34

x+y=7

3) x^2-2xy-y^2=1

x+y=2

1) x^2+y^2=74

X=2+y

(2+y) ^2+y^2=74

4+4y+y^2+y^2=74

2y^2+4y-70=0Y^2+2y-35=0D=4+140=144

y1=5

y2=-7 = > x1=2+5=7; x2=2 + (-7) = - 5

2) x^2+4y^2=34

x+y=7

x=7-y

(7-y) ^2+4y^2=34

49-14y+y^2+4y^2-34=0

5y^2-14y+15=0

D=196-300=-104

Корней нет

3) x^2-2xy-y^2=1

x+y=2

y=2-xx^2-2x * (2-x) - (2-x) ^2=1

x^2-4x+2x^2-4-4x+x^2-1=0

4x^2-8x-5=0

D=64+80=144

x1=2,5; x2=-0,5;

y=2-x = > y1=2-2,5=-0,5; y2=2 - (-0,5) = 2+0,5=2,5