16: Derivative is

Critical points:

f ′ is suspect at x = 2.

Since f is continuous at 2, we can connect the middle two intervals, so f is decreasing on [−1,5].

Local maximum f (−1) = 17; local minimum f (5) = −27.

Remark: One-sided derivatives at the connecting point are

Thus there is derivative at 2, f ′(2) = −9.

Now determine concavity using f ′′.

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Answer