高中课本第四册讲到数列问题,课本里也详细推论了等差、等比数列的通项、求和公式,并在课后的练习里安排了用数学归纳法证明它们的习题。但同学们课外做习题或在竞赛当中,却往往碰到一些既非等差,又非等比的数列(它们实际上也无须用多少等差、等比数列公式甚至根本 In the fourth volume of high school textbooks, the problems of series are discussed. In the textbooks, the equations of commonality, geometric progression, and summation equations are also inferred. In the exercises after class, mathematical exercises are used to prove their problems. However, when students are doing exercises outside of class or in competitions, they often encounter a series of numbers that are neither equal in arithmetic nor equal in number (they do not actually need to use much arithmetical error, etc.