Xy-y=12 xy-y^2=0 решить методом сложения

Xy - y = 12
Xy - y^2 = 0
•••••
- xy + y = - 12
- xy + xy + y - y^2 = - 12 + 0
y^2 - y - 12 = 0
D = 1 + 48 = 49 = 7^2
y1 = ( 1 + 7 ) : 2 = 4
y2 = ( 1 - 7 ) : 2 = - 3
•••••••
xy - y = 12
y( x - 1 ) = 12
X - 1 = 12 : y
X = ( 12 : y ) + 1
X1 = ( 12 : 4 ) + 1 = 4
X2 = ( 12 : - 3 ) + 1 = - 3
ответ ( 4 ; 4 ) ; ( - 3 ; - 3 )