已知一扇形的圆心角为
,半径为R,弧长为l.
(1)若
,
,求扇形的弧长l;
(2)若扇形周长为20cm,当扇形的圆心角
为多少弧度时,这个扇形的面积最大?
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e170f206fdbbd834aad7580c727e2cc6.png)
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/97cf714ffb3fd5917a76b191640b55fe.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eb1cf5f77754c603e1b1cb1927db4952.png)
(2)若扇形周长为20cm,当扇形的圆心角
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e170f206fdbbd834aad7580c727e2cc6.png)
更新时间:2020-02-13 17:33:46
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解题方法
【推荐1】已知
的始边为
轴非负半轴,终边与以原点为圆心的单位圆分别交于
两点.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/22/9eefceb5-a787-4ec5-b23a-a00d37a28ccd.png?resizew=237)
(1)如图1,若
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;
(2)如图2,若
,设
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的圆弧长.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c4e288596fa3811dd2c17bded60e82e7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f6bce3d91ca23b86d8c6625f2632e437.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/22/9eefceb5-a787-4ec5-b23a-a00d37a28ccd.png?resizew=237)
(1)如图1,若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3dbdaaa71b61b8979902d5710440c044.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/51d611603cc00e1ccde6ff95e3944041.png)
(2)如图2,若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a879721367a8f2609d13bd22393a3188.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c24095e409b025db711f14be783a406c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e648ebd598725b490a973c4ebc89a9bf.png)
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【推荐2】半径为12cm的轮子,以400r/min的速度按顺时针方向旋转.
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(2)求轮沿上的点
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名校
解题方法
【推荐1】如图,在平面直角坐标系
中,角
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![](https://img.xkw.com/dksih/QBM/editorImg/2023/12/24/a2df5d20-978d-4af3-a974-204b27aa0171.png?resizew=167)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7ee31829d0d4d5f779a957d7df8058ab.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e170f206fdbbd834aad7580c727e2cc6.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/12/24/a2df5d20-978d-4af3-a974-204b27aa0171.png?resizew=167)
(1)若点B的横坐标为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/af6ddf31b7d9225a4239883af72d153b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6cc9750c313ee972124cb62c4a6fb7ea.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/866b81a8384cce4f24867baca2e6820c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e170f206fdbbd834aad7580c727e2cc6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5b5858ee1ce52b251816757257a11c29.png)
(3)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b15163832f2f0665addd702f5e1ad671.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e170f206fdbbd834aad7580c727e2cc6.png)
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【推荐2】已知扇形的周长为20 cm,当它的半径和圆心角各取什么值时,才能使扇形的面积最大?最大面积是多少?
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