Curvature

Overview

Let $f$ be a function of a single variable defined on interval $[a,b]$. We say $f$ is convex (or convex downward or concave upward) on $[a,b]$ if every chord joining two points on its graph lies above the graph. We say $f$ is concave (or concave downward or convex upward) on $[a,b]$ if instead every chord joining two points on its graph lies below the graph.