1　 问题背景在学习了等差数列以后 ,有一类关于两个等差数列前 n项和比值的问题 ,学生由于认知结构方面的原因 ,求解时常常会出现这样或那样的错误 .怎样帮助他们正确地认识等差数列的概念和性质 ,有效地走出错误呢 ?笔者在建构主义理论的指导下 ,以自主学习为前提 ,以合作交 1 Problem Background After learning the arithmetic progression, there is a question about the first n terms and the ratio of two equal arithmetic progressions. Because of the cognitive structure, students often have one or more errors in their solution. How can they be helped? Correctly understand the concept and nature of arithmetic progression, and effectively get out of the mistakes? Under the guidance of constructivism theory, the author takes self-study as a precondition and cooperates with