对于给定条件下的代数式求值问题,如果能根据题目的特点,挖掘出已知条件和待求式之间的内在联系,往往可避繁就简,获得快捷而又准确的解答.以下就几种常见的求值方法举例说明. For algebraic expression evaluation under a given condition, if the internal relationship between the known conditions and the pending formula can be excavated according to the characteristics of the topic, it is often possible to avoid complications and to obtain a quick and accurate answer. Several common evaluation methods illustrate.