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在教学圆的周长和面积这一单元时,由于计算比较繁,学生很容易出错,但在计算过程中,教师若指导学生对“π”进行灵活处理,就可化繁为简,化难为易。一、让学生记住1π-9π的值(取π≈3.14)。1π=3.14 2π=6.28 3π=9.42 4π=12.565π=15.70 6π=18.84 7π=21.98 8π=25.129π=28.26二、记住这些值以后,要求学生在计算过程中不要急于将“π”写成3.14,将其结果用“几π”的形式表示,然后根据记忆的数值,直接写出计算结果。如:例1:一个圆的半径是2.5厘米,它的周长和面积各是多少?
When teaching the perimeter and area of the circle, the students are easy to make mistakes due to the more complicated calculations. However, in the process of calculation, if the teacher guides the students to flexibly handle the “π” Difficult for easy. First, let students remember the value of 1π-9π (take π ≈ 3.14). 1π = 3.14 2π = 6.28 3π = 9.42 4π = 12.565π = 15.70 6π = 18.84 7π = 21.98 8π = 25.129π = 28.26 Second, remember these values, require students in the calculation process do not rush to write “π” 3.14, the result of “a few π ” in the form of said, and then according to the value of the memory, write the calculation results directly. Such as: Example 1: A radius of a circle is 2.5 cm, its circumference and area of each is how much?