我国伟大的数学家刘徽于公元263年攥《九章算术注》中指出,“周三径一”不是圆周率值,实际上是圆内接正六边形周长和直径的比值(如图1).刘徽发现,圆内接正多边形边数无限增加时,多边形的周长就无限逼近圆周长,从而创立“割圆术”,为计算圆周率建立起相当严密的理论和完善的算法.如图2,六边形
是圆内接正六边形,把每段弧二等分,可以作出一个圆内接正十二边形,点
为
的中点,连结
交
于点
,若
,则
的长为( )
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更新时间:2024-01-01 08:44:00
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【推荐1】正三角形
的边长为
,
是边
上一动点,
两点关于直线
对称,连接
并延长交直线
于
,连接
,在点
运动过程中,
的最大值是( )
![](https://img.xkw.com/dksih/QBM/editorImg/2023/2/15/63085571-d3c7-4d6e-8344-d4452bbe840c.jpg?resizew=159)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
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【推荐2】如图,菱形ABCD中,∠A=60°,AB=3,⊙A、⊙B的半径分别为2和1,点P、E、F分别是边CD、⊙A和⊙B上的动点,则PE+PF的最小值是( )
![](https://img.xkw.com/dksih/QBM/editorImg/2022/12/23/ac952b0a-3338-49fb-a988-f67d1c4b5e83.png?resizew=175)
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【推荐1】如图,
中,斜边
,内切圆I切各边为D,E,F,连结
,作
交
于G,则
长为( )
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【推荐2】如图,在
中,点D是边
上的中点,连接
,将
沿着
翻折,得到
,
与
交于点F,连接
.若
,则点C到
的距离为( )
![](https://img.xkw.com/dksih/QBM/2021/5/28/2730648994865152/2730688395419648/STEM/945a60a8-c930-46c7-a90f-2c4539977b6c.png)
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【推荐1】如图,正六边形A1B1C1D1E1F1的边长为2,正六边形A2B2C2D2E2F2的外接圆与正六边形A1B1C1D1E1F1的各边相切,正六边形A3B3C3D3E3F3的外接圆与正六边形A2B2C2D2E2F2的各边相切,…按这样的规律进行下去,A10B10C10D10E10F10的边长为( )
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【推荐2】如图,
为正六边形
边上一动点,点
从点
出发,沿六边形的边以1cm/s的速度按逆时针方向运动,运动到点
停止.设点
的运动时间为
,以点
、
、
为顶点的三角形的面积是
,则下列图像能大致反映
与
的函数关系的是( )
![](https://img.xkw.com/dksih/QBM/2022/1/14/2894289601323008/2895524525195264/STEM/366096b0-4311-412a-a457-90033ca30f56.png?resizew=157)
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【推荐1】将一张以
为边的矩形纸片,先沿一条直线剪掉一个直角三角形,在剩下的纸片中,再沿一条直线剪掉一个直角三角形(剪掉的两个直角三角形相似但不全等),剩下的是如图所示的四边形纸片
,其中
,则剪掉的两个直角三角形的斜边长不可能是( ).
![](https://img.xkw.com/dksih/QBM/editorImg/2024/2/27/53106ba1-d63a-409f-8507-09356ca89004.png?resizew=134)
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真题
【推荐2】如图,
是等腰直角三角形,
,
,点
,
分别在
,
边上运动,连结
,
交于点
,且始终满足
,则下列结论:①
;②
;③
面积的最大值是
;④
的最小值是
.其中正确的是( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
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