22: Derivative is

Critical points: f = 0 for x = −1 and x = 1; f ′ is suspect at x = 0.

Local maximum f (0) = 0; local minimum f (−1) = −2 and f (1) = −2.

Remark: One-sided derivatives at the connecting point are

They are not equal, so there is really no derivative at x = 0.

Now determine concavity using f ′′.

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Answer