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Mr. Lyon was trying to find the points of inflection for . Since no value of existed such that , he assumed there was no change in concavity. Andrew said that a point of inflection exists where the second derivative changes sign. Who is correct and why? Use the second derivative and the graph of to verify your answer.

CANDIDATES for points of inflection can be found where and where DNE. You must check both.

Notice that there is not a concavity change at the cusp.