Answer
See graph, local maximum $(0,0)$, local minima $(-2.12, -20.25)$, $(2.12, -20.25)$.
increasing on $(-2.12, 0), (2.12, 4)$ decreasing. on $(-4, -2.12), (0, 2.12)$.
Work Step by Step
Step 1. See graph for $f(x)=x^4-9x^2$ over $(-4,4)$
Step 2. We can approximate: local maximum $(0,0)$, local minima $(-2.12, -20.25)$, $(2.12, -20.25)$.
Step 3. We can determine that $f$ is increasing on $(-2.12, 0), (2.12, 4)$ decreasing. on $(-4, -2.12), (0, 2.12)$.
