- (D) At x = a, f ′ changes from increasing (f ′′ > 0) to decreasing (f ′′ < 0). Thus f changes from
concave upward to concave downward, and therefore has a point of inflection at x = a. Note
that f is differentiable at a (because f ′(a) exists) and therefore continuous at a.
dmanu
(dmanu)
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