有些题目不能用定理直接证明,要用一些代换技巧,有些题目除了用到有关定理外还要用到一些代换技巧,才能证明结论。因此在平时几何学习时要掌握集中常用的代换技巧,这样才有利于提高学习解决问题。 一、等角代换 例1:如图1,AF∥DE,AB⊥DE于B,CD⊥AF于C,EF交AB于M,交CD于N, 求证: Some questions can not be directly proved with the theorem, to use some substitution techniques, some topics in addition to the use of the relevant theorem also need to use some substitution techniques to prove the conclusion. Therefore, in the usual geometry to learn to concentrate on the common substitution skills, so as to help improve learning to solve the problem. First, the equilateral substitution Example 1: As shown in Figure 1, AF ∥ DE, AB ⊥ DE in B, CD ⊥ AF in C, EF cross in M, pay CD in N, verify: