11: Derivative is
Critical points: f = 0 for x = −1; f ′ is suspect at x = 0.
Local maximum f (−1) = 1/e; local minimum f (0) = 0.
Remark: One-sided derivatives at the connecting point are
They are not equal, so there is no derivative at x = 0.
Now determine concavity using f ′′.
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