对于一个新的或难度较大的问题。如果已知与未知之问在短时间内看不出它们的联系。那么再进一步观察。再深入一层思考,再广泛地联想。突然发现:引进一个新的变量或通过对已知条件的转化,问题就简单得多了。这就是换元的思想。换元法是借助引入新变元来实现问题转化的一种解题方法。新变元的引人没有固定的形式,它依赖于问题的结构和特点。三角代换是最常见的换元形式之一。我们先来看这样一组问题—— For a new or more difficult problem. If the known and unknown asked in a short period of time can not see their connection. Then further observation. Then a deeper layer of thinking, and then widely Lenovo. Suddenly discovered that the problem is much simpler to introduce a new variable or to transform known conditions. This is the idea of ​​changing yuan. Redemption method is to solve the problem by introducing a new argument to solve a problem-solving method. The introduction of the new argument has no fixed form, it depends on the structure and characteristics of the problem. Triangular substitution is one of the commonest forms of commutation. Let us first look at such a group of issues -