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案例:在教完长方体的体积后,教材安排了这样一道习题:一块长方形铁皮,长40厘米,宽20厘米,像图1那样从四个角切掉边长为5厘米的正方形,
Case: After teaching the volume of the cuboid, the textbook has arranged such a problem: A rectangular sheet of metal with a length of 40 cm and a width of 20 cm, cut squares of 5 cm in length from four corners as in Figure 1,