DefinitionIn calculus, Riemann sums are methods for approximating the total area under a curve on a graph, otherwise known as the integral of a function. They represent the sum of rectangles or trapezoids that estimate the area. Example: The left Riemann sum is an approximation of ∫abf(x)dx by adding the areas of f(xi)Δx where i=0,1,...,n−1, and Δx=nb−a.