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## 'Patterns of Inflection' printed from http://nrich.maths.org/

A point of inflection of a curve $y=f(x)$ is a point at which
the second derivative $\frac{d^2y}{dx^2}$ changes sign.

Geometrically, you can think of a point of inflection as a point
where the tangent to the curve crosses the curve.

Points of inflection need not also be stationary points (first
derivative also zero), although they might be.