int k=__gcd(y2-y1,(x2-x1)*(x2-x1)) ;

cout << (x2-x1)*(x2-x1)/k << "y = " << (y2-y1)/k << "x^2 + " << ((-2)*x1*(y2-y1))/k << "x + " << ((y2-y1)*x1*x1+y1*(x2-x1)*(x2-x1))/k << endl ;