The value of 4126x3 dx\displaystyle {\int_{{{4}}}^{{{12}}}}{6}{x}^{{3}}\ {\left.{d}{x}\right.} may be determined by calculating the limit of a regularly partitioned Riemann sum with circumscribed rectangles of the formlimnk=1n6ck3 Δx\displaystyle \lim_{{{n}\to\infty}}{\sum_{{{k}={1}}}^{{n}}}{6}{{c}_{{k}}^{{3}}}\ \Delta{x} =limnk=1n(AΔx+BΔx2+CΔx3+DΔx4)\displaystyle =\lim_{{{n}\to\infty}}{\sum_{{{k}={1}}}^{{n}}}{\left({A}\Delta{x}+{B}\Delta{x}^{{2}}+{C}\Delta{x}^{{3}}+{D}\Delta{x}^{{4}}\right)} where

limnk=1nAΔx=\displaystyle \lim_{{{n}\to\infty}}{\sum_{{{k}={1}}}^{{n}}}{A}\Delta{x}=  

limnk=1nBΔx2=\displaystyle \lim_{{{n}\to\infty}}{\sum_{{{k}={1}}}^{{n}}}{B}\Delta{x}^{{2}}=  

limnk=1nCΔx3=\displaystyle \lim_{{{n}\to\infty}}{\sum_{{{k}={1}}}^{{n}}}{C}\Delta{x}^{{3}}=  

limnk=1nDΔx4=\displaystyle \lim_{{{n}\to\infty}}{\sum_{{{k}={1}}}^{{n}}}{D}\Delta{x}^{{4}}=