“圆的周长和面积”,这部分内容的基本概念较多而且很抽象,公式多而杂。这对学生来说自然成了学习的难点。教材上的公式有:d=2r、r=d/2、c=πd、c=2πr、S=πr~2、S=πr~2/360×n。教师在教学中又常常加上d=c/π、r=c/2π。这样,学生在解决有关实际问题时,因为公式多不便于记忆,所以,往往出现乱套公式的现象。有时一题需要几步计算,学生更是一筹莫展,不知究竟选用那几个公式?先用那个公式,后用那个公式? 对此,建议在学生学完这一部分内容后,帮助学生找出半径、直径、周长、面积之间的内在联系, “Circle circumference and area”, the basic concept of this part of content is more and more abstract, the formula is more and more complicated. This is naturally a difficult learning point for students. The formula on the textbook is: d = 2r, r = d / 2, c = πd, c = 2πr, S = πr ~ 2, S = πr ~ 2/360 × n. Teachers in teaching often add d = c / π, r = c / 2π. In this way, students often solve the problem of formulating formulas when solving practical problems because the formulas are inconvenient to memorize. Sometimes a question needs a few steps to calculate, the student is even more helpless, I do not know whether to choose which formula? Use that formula first, then use that formula? In this regard, it is recommended that students finish this part of the content to help students find out the radius, Diameter, perimeter, the intrinsic link between the area,