(=) x - xy - y - 1 = 0
(=) (xy - x) + (y - 1) = 0
(=) x(y - 1) + (y - 1) = 0
(=) (x + 1) . (y - 1) = 0
(=) \(\left[{}\begin{matrix}x=1\\y=-1\end{matrix}\right.\)
Với x = 1 có : x -1 = y - 1 (=) ∀ y ∈ R
Với y = -1 - y = -y - 1 (=) ∀ x ∈ R
Vậy pt có no : \(\left\{{}\begin{matrix}x=1\\y=-1\end{matrix}\right.\)