Here's the question you clicked on:
agentx5
I guess I'm not understanding the concept for part of this, what should I know? I'm posting my answers below, I would like to know what I did incorrectly in the middle part. Yes I realize this is about identifying concavity and how to do that, but I want to know how to do the notation as shown, what that means I need to do mathematically, in steps. I'll be back tomorrow to check on this :-)
So to find the second derivative of a parametric, I need to do what in what order, basically. The textbook is kind of a fail on this explaining this part and it's not covered in the lecture.
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So your second derivative isn't right.
Perfect, I understand much better now @mahmit2012 :-D Now I just need to remember those steps for future problems!