Probar que $$ y_{n}=\Big(1+\frac{1}{n}\Big)^{n}$$ es creciente.
Intente por el desarrollo del binomio de Newton , asi obtuve:
$$ \begin{align*}
y_{n}&= 1+ \sum_{k=1}^{n} \Big(1- \frac{k-1}{n} \Big)\Big(1- \frac{k-2}{n} \Big) ...... \Big(1- \frac{1}{n} \Big) \frac{1}{k!} \\
y_{n+1}&= 1+ \sum_{k=1}^{n+1} \Big(1- \frac{k-1}{n+1} \Big)\Big(1- \frac{k-2}{n+1} \Big) ...... \Big(1- \frac{1}{n+1} \Big) \frac{1}{k!} \\
y_{n+1}-y_{n}&= \sum_{k=1}^{n} \Big[ \Big(1- \frac{k-1}{n+1} \Big)\Big(1- \frac{k-2}{n+1} \Big).. \Big(1- \frac{1}{n+1} \Big)- \Big(1- \frac{k-1}{n} \Big)\Big(1- \frac{k-2}{n} \Big) ... \Big(1- \frac{1}{n} \Big) \Big] \frac{1}{k!} \\
&=+ \Big(1- \frac{n}{n+1} \Big)\Big(1- \frac{n-1}{n+1} \Big)...\Big(1- \frac{1}{n+1} \Big)\Big(1- \frac{1}{n+1} \Big)
\end{align*} $$
Mi duda es, como garantizo que la parte de corchetes es positivo