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Section 4.10 \(\epsilon\)-\(\delta\) Definitions

The limit statement
\begin{equation*} \lim_{x \rightarrow a} f(x) = L \end{equation*}
means: \(\forall \epsilon \gt 0\text{,}\) \(\exists \delta > 0\) such that if \(|x-a| \lt \delta\) then \(|f(x) - L| \lt \epsilon\text{.}\)
The limit statement
\begin{equation*} \lim_{x \rightarrow a} f(x) = \infty \end{equation*}
means: \(\forall N \in \NN\text{,}\) \(\exists \delta \gt 0\) such that if \(|x-a| \lt \delta\) then \(f(x) \gt N\text{.}\)
The limit statement
\begin{equation*} \lim_{x \rightarrow \infty} f(x) = L \end{equation*}
means \(\forall \epsilon \gt 0\text{,}\) \(\exists N \in \NN\) such that if \(x \gt N\) then \(|f(x) - L| \lt \epsilon\text{.}\)
The limit statement
\begin{equation*} \lim_{x \rightarrow \infty} f(x) = \infty \end{equation*}
means: \(\forall N \in \NN\text{,}\) \(\exists M \in \NN\) such that if \(x \gt M\) then \(f(x) \gt N\text{.}\)