常值代换的妙用马明义（甘肃省静宁县一中７４３４００）对于有限制条件：ｆ（ｘ，ｙ，…）＝ｃ（其中ｃ为常数）的数学问题，通常的思路是消元代入或整体代入，但这种做法往往因运算量偏大，不易奏效．若反其道而行之，将常数ｃ用ｆ（ｘ，ｙ，…）代替，则可收到事半功倍... The magical application of constant value substitution Ma Mingyi (Jianning County, Gansu Province, China No. 743400) For mathematical problems with restrictions: f(x,y,...)=c (where c is a constant), the general idea is to replace or replace Replaced, but this approach is often due to the large amount of computation, not easy to work. If you do the opposite, replace the constant c with f(x,y,...) and you will receive more