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交叉递推数列是指据条件,交叉使用两个不同的递推公式确定的数列,目前这类问题涉及的递推公式较为简单,一般为等差或等比数列,而选取递推公式的条件设置较为灵活,形式多样,常见有以下几种形式.1由n的奇偶性选择递推公式例1.(2012高考全国卷)数列{a_n}满足a_(n+1)+(-1)~na_n=2n-1,则{a_n}的前60项和为.分析:由a_(n+1)+(-1)~na_n=2n-1,可得
The cross-recursive number sequence refers to the number sequence determined by crossing two different recursion formulas according to the conditions. Currently, the recursion formulas involved in such problems are relatively simple, usually in the form of arithmetic or geometric ratios, and the conditions for selecting recurrence formulas Set a more flexible and diverse forms, common in the following forms.1 The choice of recursive formula by the parity of n Example 1. (2012 national college entrance examination) sequence {a_n} to meet a_ (n + 1) + (- 1) ~ na_n = 2n-1, then the first 60 terms of {a_n} are: Analysis: From a_ (n + 1) + (-1) to na_n = 2n-1,