I am really struggling with these types of questions. So if you've got the time, a way to solve these types of questions in general would be really helpful!
Right, the specific question goes as follows:
Given that P = 2x + 100/x
Find the value of x for which P is minimum.
Use the second derivative to justify your answer.
I have no clue how to go about doing this, let alone what a second derivative is.