\[ \begin{split} &\lim_{n \to \infty} (1+2^n-3^n)=\\[16pt] &=\lim_{n \to \infty} 3^n\left(\frac{1}{3^n}+\left(\frac{2}{3}\right)^n-1\right)=\\[16pt] &=-\lim_{n \to \infty} 3^n=-\infty \end{split} \]