Possibly the simplest version of numerical integration. If a definite integral ${\int }_a^{b}f\left(x\right)\text{d}x$ is to be calculated using n strips of width h = (b–a)/n then the area under the curve is replaced by a series of rectangles of width h with height equal to the value of the function at its midvalue. Labelling the midpoints m₁, m₂,…, m_n gives the approximation