a) $(-\infty,-1)$ & $(3,\infty)$ b) $(-1,3)$
Work Step by Step
Step 1: Graphically find the values where $f'(x)$ is equal to $0$, positive & negative. Step 2: $f(x)$ is increasing where $f'(x)$ is positive. Step 3: $f(x)$ is decreasing where $f'(x)$ is negative. Note: The answer is in interval notation.