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4.3 圆面积

4.3 圆面积. 期末倒计时. 把一个圆 12 等分. 对半分. 半个圆先拼接. 另外半个继续拼接. 最后一片处理一下就成. 对半开. （注： C=2πr ）半个圆周长 πr. 6. 1. 2. 3. 4. 5. r. 圆的面积近似可以看成长方形面积. S=πrxr=πr 2. 圆的半径扩大 3 倍，面积扩大几倍？ 假设原来的半径为 r , 那么 S=π r 2 扩大三倍后半径为 3r ，那么 S=πx3rx3r=9πr 2 ∴ 是原来的 9 倍。 那么直径扩大 3 倍呢？

aaron-roberts
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4.3 圆面积

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  1. 4.3圆面积

  2. 期末倒计时 把一个圆12等分

  3. 对半分

  4. 半个圆先拼接

  5. 另外半个继续拼接 最后一片处理一下就成

  6. 对半开

  7. （注：C=2πr）半个圆周长πr 6 1 2 3 4 5 r

  8. 圆的面积近似可以看成长方形面积 S=πrxr=πr2

  9. 圆的半径扩大3倍，面积扩大几倍？ 假设原来的半径为r ,那么S=π r 2 扩大三倍后半径为3r，那么S=πx3rx3r=9πr 2 ∴是原来的9倍。 那么直径扩大3倍呢？ 【结论】圆面积S与圆的半径r或者直径d扩大、缩小的倍数成平方关系。

  10. 环形面积=大圆面积-小圆面积 设大圆半径R、小圆半径r S圆环=πR2– π r2 =πx(R2- r2 )

  11. 已知甲圆的半径长是乙圆的直径长，且他们的面积之和是100cm2 那么甲圆的面积是多少？

  12. RESUME

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