【摘要】 定积分的微元法对微元的选取不是随意的，而是有一定要求的，如果达不到要求，得到的计算公式就是错误的.文章在强调微元的选取必须遵循|△U-f(x)dx|=o(dx)(dx→0)的基础上，对面积、体积、侧面积计算公式中的微元选取进行了详细的分析，并做了严格的证明.更多还原

【Abstract】 In the differential element method of definite integral, the selection of micro-elements is not arbitrary, but determined by certain requirements. If the requirements are not met, the calculation formulas obtained are wrong. On the basis of emphasizing that the selection of micro-elements must follow the following rule:|ΔU-f(x)dx|=o(dx),dx→0, the paper analyzes the selection of microelements in the calculation formulas of area, volume and lateral area in detail, and makes a strict proof.更多还原