We studied Apex Calculus for this topic. However, Active Calculus addresses it as well, from a slightly different point of view. Quotation from Active Calculus Section 5.6.3: "using trapezoids to estimate the (signed) area bounded by a curve is the same as averaging the estimates generated by using left and right endpoints." Which of the following expresses this result with notation? OT = L + R O T = L + R O T = [Ln + Rn]