This isn't quite homework, but still stuff I don't understand.

1- f(x) = 4x^2

0 < x ≤ 8

I understand that there's no local max, and that the absolute max is 256. But for local and absolute minimums I don't quite understand. How to find the min values. If I find the critical value and don't include 0, then there's no critical value, which means I don't understand how to find the mins.

Same thing with this one:

g(t) = | 4t - 9 |

g'(t) is 4. Which, as far as I know, doesn't mean there's a critical point.

One more question:

x^(-4)*ln(x)

Product rule. Right. But isn't the derivative of the left hand function x^(-4)*ln(-4), which doesn't exist because you can't take the log of a negative number?