  It is a generalization of Pell's equation $x^2-Dy^2=0$. Here, we show that:
if our Diophantine equation has a particular integer solution and $ab$ is not a
perfect square, then the equation has an infinite number of solutions; in this
case we find a close expression for $(x_n,y_n)$, the general positive integer
solution, by an original method. More, we generalize it for any Diophantine
equation of second degree and with two unknowns $f(x,y)=0$.
