用数值代替代数式里的字母，计算后所得的结果，叫做代数式的值．求代数式的值是初中代数的常见题型．下面介绍这类问题的一些常见解法．一、直接代入法把条件中所给字母的值，直接代人代数式里计算求值，这是最基本的方法．例1当。一一回，b一一2时，代数式aZ一？的值是．（19 Substituting numerical substitutions for the letters in the formula, the results obtained are called algebraical values. Finding algebraic expressions is a common question for junior high school algebras. Here are some common solutions to this type of problem. First, the direct substitution method takes the value of the letter given in the condition and calculates the evaluation directly in the algebraic formula. This is the most basic method. Example 1 when. One by one, b - one two, algebraic aZ one? The value is (19