数列中常数存在性问题是高考的热点,中学生的难点,这类问题常以方程、不等式为载体,在知识的交汇处考查综合运用能力,抓住特殊与普遍,近似与精确,有限与无限之间的关系进行转化是解决这类问题的关键． The problem of existence of constants in the series is a hot spot of the college entrance examination. Difficulty of middle school students. This type of problem often uses equations and inequalities as the carrier to examine comprehensive utilization skills at the intersection of knowledge, grasp special and universal, approximate and precise, finite and infinite. The transformation of the relationship is the key to solving such problems.