如图,菱形ABCD的边长为2,BD=2,E、F分别是边AD,CD上的两个动点,且满足AE+CF=2.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/8/15/cee83aff-4851-4eb3-acf2-76093ceabee0.png?resizew=176)
(1)求证:△BDE≌△BCF;
(2)判断△BEF的形状,并说明理由;
(3)设△BEF的面积为S,求S的取值范围.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/8/15/cee83aff-4851-4eb3-acf2-76093ceabee0.png?resizew=176)
(1)求证:△BDE≌△BCF;
(2)判断△BEF的形状,并说明理由;
(3)设△BEF的面积为S,求S的取值范围.
更新时间:2022-08-14 11:35:44
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解答题-问答题
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【推荐1】如图1,在锐角三角形ABC中,点D在边BC上,过点D分别作线段AC,AB的垂线,垂足为点E、F.如果
,那么我们把AD叫做△ABC关于
的正平分线.
![](https://img.xkw.com/dksih/QBM/2022/6/17/3003467663425536/3006275859734528/STEM/23a6fb0423d141f8878eccd3a194931a.png?resizew=509)
(1)如图2,
,
,
,试说明AD为△ABC关于
的正平分线;
(2)如图3,若AD为△ABC关于
的正平分线,过点D作
,
,
.
①试说明:四边形MNFD为正方形;
②若
,边AB上的高为80,
,求
的正平分线AD的长.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f19f47c581c22f73b166f58fb9ce12a3.png)
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(1)如图2,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/047dc9795efa99b6fb9fdf9778085dab.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a1e0b41cd45fba881194a02ec19bc26e.png)
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(2)如图3,若AD为△ABC关于
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/21b28f28ced0531d1df34fcf04c6c67f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7aa30a9ee227af2b387cf6e028c20d7d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ef3a7d7da25b68cedf81462ea2b0ed16.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f479d987bc7abd828c64f9dc745836ab.png)
①试说明:四边形MNFD为正方形;
②若
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6e071479287e774f7f0990b1a649658f.png)
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解答题-作图题
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解题方法
【推荐2】如图是
的正方形网格,请仅用无刻度的直尺按要求完成以下作图(保留作图痕迹).
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(1)在图1中作
的角平分线;
(2)在图2中过点
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,使点
,
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0fb9d60d456560e9bac66c8b20c49bb1.png)
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(1)在图1中作
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d39b8d91afc34e4a9b0fdbb6bafb9087.png)
(2)在图2中过点
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解答题-证明题
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适中
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【推荐1】两个角的边交于点
(如图),已知这两角的平分线互相垂直.求证:
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解答题-证明题
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【推荐2】如图,
为
的直径,弦
平分
交
于
,
为
延长线上一点且
.
(1)求证:
为
的切线;
(2)若
,
,求
的半径及
的长.
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(2)若
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