Х - Y = 7
X = Y + 7
X^2 = ( Y + 7)^2 = Y^2 + 14Y + 49
-----------------------------------------
X^2 + Y^2 = 9 - 2XY
Y^2 + 14Y + 49 + Y^2 = 9 - 2Y*( Y + 7)
2Y^2 + 14Y + 49 = 9 - 2Y^2 - 14Y
2Y^2 + 2Y^2 + 14Y + 14Y + 49 - 9 = 0
4Y^2 + 28Y + 40 = 0
--------------------------------------------
D = 784 - 640 = 144 ; V D = 12
Y1 = ( - 28 + 12 ) : 8 = ( - 16 ) : 8 = ( - 2 )
Y2 = ( - 40 ) : 8 = ( - 5 )
--------------------------------------------
X = Y + 7
X1 = - 2 + 7 = 5
X2 = - 5 + 7 = 2
-------------------------------------------
Ответ: ( 5 ; - 2 ) ; ( 2 ; - 5 )