## Precalculus (6th Edition) Blitzer

$\lt f(x_2)$ $\gt f(x_2)$ $= f(x_2)$
Recalling the definitions of increasing, decreasing and constant functions, we have: - $f$ is increasing on $I$ if $f(x_1)\lt f(x_2)$ when $x_1\lt x_2$ - $f$ is decreasing on $I$ if $f(x_1)\gt f(x_2)$ when $x_1\lt x_2$ - $f$ is constant on $I$ if $f(x_1)= f(x_2)$.