One of the most important limits in calculus is
$$\bbox[#F2F2F2,5px,border:2px solid black] {\lim_{x\to0}\left(1+{x}\right)^{1/x}=e}$$
where \(e\) is an irrational number (like \(\pi\)) and is approximately 2.718281828.
We are not going to prove that such a limit exists, but we will content ourselves by plotting \(y=(1+x)^{1/x}\) (Figure 1), and show graphically that as \(x\approx0\), the function \(y=(1+x)^{1/x}\) takes on values in the near neighborhood of \(2.718\cdots\), and therefore \(e\approx2.7182\).
As \(x\) approaches zero from the left, \(y\) decreases and approaches \(e\) as a limit. As \(x\) approaches zero from the right, \(y\) increases and also approaches \(e\) as a limit.
As \(x\to\infty\), \(y\) approaches the limit 1, and as \(x\to-1\) from the right, \(y\) increases indefinitely (see Table 1).
Let’s replace \(1/x\) by \(u\). So when \(x\to0\), we have \(u\to\infty\). Thus
\[\lim_{x\to0}(1+x)^{1/x}=\lim_{u\to\infty}\left(1+\frac{1}{u}\right)^{u}=e.\]
In other words:
$$\bbox[#F2F2F2,5px,border:2px solid black] {\lim_{x\to\infty}\left(1+\frac{1}{x}\right)^{x}=e}$$