一、背景小学里,学习过圆周长、圆面积的计算公式,知道圆周长C与半径R之间的关系为:C=2πR;圆面积S与半径R之间的关系为:S=πR~2.小学里,已经认识了圆和扇形,在本章的第一节还学习过弧的有关概念,在此基础上,引导学生感悟弧和圆、扇面和圆面间的“整体与局部”的关系,弧是圆的一部分,扇面是圆面的一部分,为在本节探索弧长计算公式、扇形面积计算公式做好铺垫.为了进一步提高学生几何推理能力、有条理的表达能力、 First, the background of the primary school, learning circumference, the circular area of ​​the formula, know the circle C and radius R of the relationship between: C = 2πR; circular area S and the radius R between the relationship: S = πR ~ 2. In primary school, we have already got to know the circle and the fan. In the first section of this chapter, we also studied the related concepts of arc. On the basis of this, we guide the students to comprehend the “whole and part of the arc and circle, ”, The arc is part of the circle, the fan surface is a part of the circular surface, in order to explore arc length calculation formula in this section, fan area formula to pave the way.In order to further improve students’ ability of geometric reasoning, orderly expression,