Download - 圆的面积
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樊家村小学 陈俐彤
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高 宽
底 长
推导过程: 长方形的面积 = 长 ×宽
平形四边形的面积 = 底 ×高
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高 宽
底 长
推导过程: 长方形的面积 = 长 ×宽
平形四边形的面积 = 底 ×高
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继续
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长 = r
宽 = r
思考: 1、圆同拼成的近似长方形什么变了?什么没变?2、拼成的近似长方形的长相当于圆的哪一部分?宽相当圆的哪一部分? 3、你能不能根据它们的以上关系由长方形面积计算公式推导出圆的面积计算公式?写出推导过程。
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C16
3
C16
5
r2
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天坛的圜丘最高的一层是半径 15 米的圆,这层的面积是多少平方米?
已知: r=15 米
S=πr 2
平方米)(5.7061514.3 2 答:圜丘最高一层的面积是 706.5平方米。
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公园绿地里浇水用的喷头,最远能喷水 5 米。喷头旋转一周,最大的喷水面积有多少平方米 ?