等差数列、等比数列是最基本的两种数列,我们从定义(递推公式)、通项公式、前n项和公式、性质等方面对它们进行了深入的研究.而对其他不太了解的数列,我们经常将它们转化为等差数列或等比数列,再进行探讨.但在转化的过程中,有时为了探明方向的可行性,需要预设一些未知数,于是待定系数法就派上用场了. Equal-difference series, geometric series is the most basic two series, we define (recursive formula), the general formula, the first n terms and formulas, their nature and so on they conducted a thorough study. We often transform them into arithmetic or geometric series, and then discuss them, but in the process of transformation, we sometimes need to preset some unknowns in order to find out the feasibility of the direction, so the method of determining the coefficient to be determined Come in handy