\[ \begin{split} &\lim_{n \to \infty} \left(\frac{n^2+6}{n^2}\right)^{n^2}=\\[6pt] &=\lim_{n \to \infty} \left(1+\frac{6}{n^2}\right)^{n^2}=\\[6pt] &=\lim_{n \to \infty} \left[\left(1+\frac{6}{n^2}\right)^{\dfrac{n^2}{6}}\right]^6=\\[6pt] &=e^6 \end{split} \]