Mutually inverse substitution is only add 0 or times 1 to the formula in the course of solving problems, but use properly, therefore can overcome a lot of difficulties, enable solving the course of questions to simplify greatly.

• 互逆代换在解题过程中尽管仅是在式中加上0或乘以1,但只要运用适当,由此即可克 服许多困难,使解题过程大大简化。