Why a zero second derivative isn't your only inflection point

Mistakes when finding inflection points: second derivative undefined | AP Calculus AB | Khan Academy · 6:11 · Video: Khan Academy · Watch at the source

In short: Finding where a curve changes concavity requires more than just solving for zero. This lesson from Khan Academy clarifies a common calculus pitfall: the critical role of undefined derivatives.

In AP Calculus AB, students often focus exclusively on points where the second derivative equals zero to identify inflection points. However, this approach is incomplete. To find every candidate for an inflection point, one must also examine locations where the second derivative is undefined.

By identifying both types of candidates—those that are zero and those that do not exist—students can ensure a comprehensive analysis of a function's curvature. This distinction is fundamental for mastering the behavior of complex graphs.

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