Consider the following.

f(x) =

1

4

x⁴

1

3

x³3x²

Find the critical numbers. (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.)

x=

Find the open intervals on which the function is increasing or decreasing. Use a graphing utility to verify your results. (Enter your answers using interval notation. If an answer does not exist, enter DNE.)

increasing
decreasing