Suppose that $$f(x) = 2 x \sqrt{3 x^2 + 1}$$

(A) Find all critical values of $f$. If there are no critical values, enter -1000. If there are more than one, enter them separated by commas.
Critical value(s) =

(B) Use interval notation to indicate where $f(x)$ is increasing.

Note: When using interval notation in WeBWorK, you use I for $\infty$, -I for $-\infty$, and U for the union symbol. If there are no values that satisfy the required condition, then enter "{}" without the quotation marks.

Increasing:

(C) Use interval notation to indicate where $f(x)$ is decreasing.
Decreasing: