给定条件求代数式的值,一般方法是先化简后代入,但仅仅这样做还不够,还应根据给定的条件和求值式的结构特点,应用不同的解法,这样能培养同学们灵活应用知识的能力和创新能力,现举一例. Given the conditions for algebraic expressions, the general approach is to simplify simplification, but it is not enough to do so, but also to apply different solutions according to the given conditions and the structural characteristics of the evaluation formula, so that students can be flexible The ability to apply knowledge and innovative capabilities is given as an example.