Analysis of information sources in references of the Wikipedia article "Jumlah Riemann" in Indonesian language version.
Left-rule, right-rule, and midpoint-rule approximating sums all fit this definition.
We chop the plane region R into m smaller regions R1, R2, R3, ..., Rm, perhaps of different sizes and shapes. The 'size' of a subregion Ri is now taken to be its area, denoted by ΔAi.