$$\begin{aligned}x^{2}+2x=n,n\in Z\\ x^{3}-13x=k,k\in Z\end{aligned}$$ alalım.
$$\begin{aligned}x^{2}=n-2x\\ x^{3}-13x=k\\ x\left( n-2x\right) -13x=k\\ \Rightarrow nx-2x^{2}-13x=k\\ \Rightarrow nx-2\left( n-2x\right) -13x=k\end{aligned}$$
$\begin{aligned}\Rightarrow \left( n-9\right) x-2n-k=0\\ \Rightarrow n=9,k=-18\\ x^{2}+2x=n\\ \Rightarrow x^{2}+2x-n=0\\ \Rightarrow x^{2}+2x -9=0\\ x_{1}x_{2}=-9\end{aligned}$