化归就是在研究和解决数学问题时采用某种方式,借助某种函数性质、图象、公式或已知条件等将问题通过变换使之转化,进而达到解决问题的一种思想。化归思想是中学数学最基本的思想方法,也是最重要的思想方法之一,在数学解题中几乎无处不在,它不仅是一种重要的解题思想,也是一种最基本的思维策略,更是一种有效的数学思维方式。应用化归思想解题时的原则是化难 To return to the nature of the problem is to study and solve mathematical problems in some way, by means of a function of nature, images, formulas or known conditions to transform the problem to transform, so as to achieve a solution to the problem of thinking. Returning to thought is the most basic way of thinking and the most important way of thinking in middle school mathematics. It is almost everywhere in mathematical problem solving. It is not only an important problem-solving thought but also a most basic way of thinking , It is an effective mathematical way of thinking. Applying to the principle of thinking when solving problems is difficult