引伸是提出问题的一种方法．一般地说，引伸始于一个已经初步理解或基本解决的问题，而后把这一问题的条件，结论按某种需要交换形式、重新组合或作一些变动，使问题横向、纵向或按预定目标发展．由于这种方法能明确地体现教师的教学意图，而且有极强的针对性，所以引伸在教学 Extensions are a way of asking questions. Generally speaking, the extension begins with a question that has been initially understood or basically solved, and then the conditions of the question, the conclusions are exchanged in a certain form, regrouped or made some changes so that the problem develops horizontally, vertically or as intended. . Because this method can clearly reflect the teacher’s teaching intentions and has a strong pertinence, it can be used in teaching.