错项相减法是课本上推导等比数列前n项和公式体现的方法,而课本上没有正式讲解,更没有举例说明应用,因而学生在解题中常常想不到,用不上,为帮助同学们解决这个问题,本文对此法进行解读.1.错位相减法及操作过程这种方法是把原数列的前n项和乘以一个因数,作一个铺助数列,把它与原数列相减 The wrong item subtraction method is derived from textbooks on the first n items and formulas, and the textbooks did not formally explain, but did not exemplify the application, so students often can not think in solving problems, do not have access to help students To solve this problem, this paper will explain this method.1. Displacement subtraction method and operation process This method is to multiply the first n items of the original number column by a factor to make a spreading sequence and subtract it from the original number column