一、起因在最近县城三家省级实验小学联合举行的六年级数学阶段目标检测中有这样一道题:将一块长30厘米,宽20厘米的长方形铁皮,焊接成一个高5厘米的无盖长方体盒子,容积最大是多少立方厘米?(铁皮厚度忽略不计)如右图,一直以来老师们都认为该题只需计算、比较两种情况,取结果最大值即可。由于平时练习过该类型题目,大多数学生做出的答案和 First, the cause In the recent county three provincial experimental primary school mathematics phase of the sixth grade joint goal of testing there is such a question: a 30 cm long and 20 cm wide rectangular iron, welded into a 5 cm high lidless rectangular box , The largest volume is the number of cubic centimeters? (Metal thickness is negligible) As the right, teachers always think that the problem only needs to calculate, compare the two cases, take the maximum result can be. As a result of the usual practice of the type of topic, most students make the answer and