Answer
$(-\infty,-2]$ and $[3,\infty)$
Work Step by Step
The function decreases in an interval when, moving from left to right, the y-values continue to get smaller for x-values in that interval. For the graph in the question, there are two intervals in which the y-values decrease.
First, the y-values decrease for all values of $x$ between $-\infty$ and $-2$. Since $-2$ is included in the interval, a square bracket will be used on its side while on the other end, the symbol $-\infty$ is always supported by a parenthesis.
Secondly, the y-values decrease for all values of $x$ between $3$ and $\infty$. Since $3$ is included in the interval, a square bracket will be used on its side while on the other end, the symbol $\infty$ is always supported by a parenthesis.
Therefore, the function decreases in the intervals $(-\infty,-2]$ and $[3,\infty)$.
