What is the name of the theorem/method for classifying extremum using second derivatives?

Question

Given a formula $f : \mathbb{R} \rightarrow \mathbb{R}$ we know that by the Interior Exrtremum Theorem that, if $f$ attains an extremum at $c \in \mathbb{R}$, then $f'(c) = 0$.

We also know that if $f''(c) < 0$ then $c$ is a maximum and that if $f''(c) > 0$ then $c$ is a minimum. Does this Lemma/Theorem have a name?

Answer 1

This is called the Second Derivative Test.