\[ \begin{split} &\lim_{n \to \infty} \left(1-\frac{1}{n^2}\right)^n=\\[16pt] &=\lim_{n \to \infty} \left(\left(1-\frac{1}{n^2}\right)^{n^2}\right)^{\frac{1}{n}}=\\[16pt] &=e^0=1 \end{split} \]