In calculus, the Mean Value Theorem is utterly essential. It basically says, “For any function that is continuous on [a,b] and differentiable on (a,b), there exists some c in the interval (a,b) such that the secant joining the endpoints of the interval [a,b] is parallel to the tangent at c.
In Beijing, you can see the mean value theorem of calculus decorating a pedestrian bridge. I believe they are trying to ensure that every Chinese student is learning calculus.
