## Calculus: Early Transcendentals (2nd Edition)

Assuming that the function $f$ is continuous and differential at all interior points of interval $I$: $\bullet$ $f$ is increasing on $I$ if $f'(x) > 0$ at all interior points of $I$. $\bullet$ $f$ is decreasing on $I$ if $f'(x) < 0$ at all interior points of $I$.