关于数列求和的问题往往使中学生感到十分棘手。虽然在课本里介绍了一些求和方法，但往往都需要一些巧思，初学者难于掌握。本文介绍的待定系数法，虽然需要进行少量的计算，但思路是很直捷 Problems concerning the summation of numbers often make middle school students feel very troublesome. Although some summation methods are introduced in textbooks, they often require some ingenuity and are difficult for beginners to master. Although the undetermined coefficient method introduced in this paper requires a small amount of calculations, the idea is very straightforward.