$\displaystyle \begin{array}{{>{\displaystyle}l}} Gọi\ M\left( a;-a^{2}\right) \in \ ( P)\\ Ta\ có\ x-y=1\Leftrightarrow a+a^{2} =1\\ \Leftrightarrow a=\frac{-1\pm \sqrt{5}}{2}\\ Vậy\ M\left(\frac{-1+\sqrt{5}}{2} ;\frac{3-\sqrt{5}}{2}\right) \ và\ M\left(\frac{-1-\sqrt{5}}{2} ;\frac{3+\sqrt{5}}{2}\right) \end{array}$