# 4-3 Using Derivatives to Analyze Graphs of Functions

## Learning Targets

You will be able to

## Concepts / Definitions

### The First Derivative Test

Suppose that $c$ is a critical number of a continuous function $f$.

- If $f’$ changes from positive to negative at $c$, then $f$ has a local maximum at $c$.
- If $f’$ changes from negative to positive at $c$, then $f$ has a local minimum at $c$.
- If $f’$ does not change sign at $c$, then $f$ has no local maximum or minimum at $c$.

### Concavity

The graph of a differentiable function $y = f(x)$ is

- Concave up on an open interval $I$ if $y’$ is increasing on $I$
- Concave down on an open interval $I$ if $y’$ is decreasing on $I$

### Concavity Test

[Suppose the graph $y = f(x)$ is twice differentiable]

- If $f’‘(x) > 0$ for all $x$ in some open interval $I$, then the graph of $f$ is concave upward on $I$
- If $f’‘(x) < 0$ for all $x$ in some open interval $I$, then the graph of $f$ is concave downward on $I$

### Point of Inflection

A point where the graph of a function has a tangent line (is differentiable) and where the concavity changes is a point of inflection.

### Second Derivative Test for Local Extrema

- If $f’(c) = 0$ and $f’‘(c) < 0$$, then $f$ has a local maximum at $x = c$.
- If $f’(c) = 0$ and $f’‘(c) > 0$$, then $f$ has a local minimum at $x = c$.

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