# Value, slope, & concavity

When sketching the graph of a function, the obvious first step is to plot a few points. Specifically, the zeros, the turning points, and the inflection points (and, for good measure, the y-intercept). But how does one connect the dots? The answer lies within three quantities: function value, slope, and concavity. In fact, it’s just their signs that matter.

The values of $\displaystyle f{\left ( x \right )}$, $\displaystyle f{'} ( x )$, and $\displaystyle f{''} ( x )$ represent function value, slope, and concavity, respectively. This table summarizes the meaning of their signs:

Value $\displaystyle = 0$ $\displaystyle > 0$ $\displaystyle < 0$
$\displaystyle f{\left ( x \right )}$ zero positive negative
$\displaystyle f{'} ( x )$ turning point increasing decreasing
$\displaystyle f{''} ( x )$ inflection point concave up concave down

Here is an example of the information that these three quantities, given by the function and its first two derivatives, provides you with: