缘起笔者最近参加了一次教研活动,聆听了一节《长方形与正方形的周长》的课程。课中,教师出示一个长6厘米、宽4厘米的长方形,学生通过自主探究,得到长方形周长的计算方法主要为以下两种:第一种:6+4+6+4(一条边一条边地加);第二种:6×2+4×2(长×2+宽×2)。这种方法是运用乘法的知识对第一种方法进行优化得到的。接着,教师在肯定了前两种方法之后引导学生观察长方形,然后 The origin of the author recently participated in a teaching and research activities, listening to a section of “circumference of the rectangle and the square” course. In class, the teacher presents a rectangle 6 centimeters long and 4 centimeters wide. The students can obtain the rectangle perimeter by self-exploration. There are mainly two ways to calculate the perimeter: the first one is 6 + 4 + 6 + 4 Plus); the second: 6 × 2 +4 × 2 (length × 2 + width × 2). This method is to use the knowledge of multiplication to optimize the first method. Then, the teacher guided the students to observe the rectangle after affirming the first two methods and then