在解决有关方程组的问题时,常常会遇到一类比较新颖的问题,那就是方程的个数少于未知数的个数的求代数式的值问题,这类问题在数学竞赛中更是活跃,有时让人感到束手无策.解决这类问题的确有一定的难度,它难就难在如何对题目所给的方程组实施运算,对这一关键问题本文给出解决的几种对策供参考. When solving the problems of the equations, we often encounter a relatively new type of problem, that is, the value of the algebraic expression of the number of equations less than the number of unknowns. Such questions are even more active in the mathematical competition. Sometimes people feel helpless. Solving such problems is indeed difficult. It is difficult to implement operations on the equations given by the subject. Several countermeasures for solving this problem are given for reference.