在代数式的运算或化简时,往往要用具体的数值代替代数式中的字母,求出代数式的值.代数式求值的方法较多,下面举例说明代数式求值的方法. In algebraic operations or simplifications, it is often necessary to substitute specific numerical substitutions for the letters in the formulas to find the values ​​of algebraic expressions. There are many methods for evaluating algebraic expressions. The algebraic expressions are evaluated by the following examples.