在很多与数列有关的题目当中,以t~n(t>1)与an~2+bn+c的大小比较这个不等式为背景的题目经常出现,在解题时,往往先要定位出某个N,先证明:当n>N时有,t~n>an~2+bn+c成立.这是解题的核心部分,也是关键的一步. Among many topics related to series, the problem of comparing the inequality as the background with t ~ n (t> 1) and the size of an ~ 2 + bn + c often appears. When solving problems, it is often necessary to locate some N, the first proof: when n> N, t ~ n> an ~ 2 + bn + c is established.This is the core part of the problem-solving, but also a crucial step.