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用数值代替代数式里的字母,按照代数式中的运算关系计算得出结果,就叫做求代数式的值.求代数式值的一般步骤是:先代入,后计算.在代入时,要注意字母与数字的对应关系.计算时,要按照先乘方,后乘除,再加减的顺序.求代数式值的一般方法包括如下几种:一、直接代入法例1求当a=3,b=时,
Substituting numeric substitutions for the letters in the formulas and calculating the results according to the algebraic expressions is called evaluating algebraic expressions. The general steps for evaluating algebraic expressions are: Substituting them first and then calculating them. When substituting them, pay attention to the letters and numbers. Correspondence relations. In calculations, we must follow the order of the first power, the post-multiplication, and the addition and subtraction. The general methods for finding algebraic values include the following: 1. Directly substitute the law 1 for a=3, b=,