如图,在△ABC中,AB=AC,点D,E,F分别在AB,BC,AC上,且BD=CE, BE=CF.
![](https://img.xkw.com/dksih/QBM/2020/12/10/2611278284292096/2611424062316544/STEM/998802d69d0e42c6a570540bd6b959dc.png?resizew=100)
(1)求证:△DEF是等腰三角形.
(2)当∠A=60°,DE=6,求△DEF的周长.
![](https://img.xkw.com/dksih/QBM/2020/12/10/2611278284292096/2611424062316544/STEM/998802d69d0e42c6a570540bd6b959dc.png?resizew=100)
(1)求证:△DEF是等腰三角形.
(2)当∠A=60°,DE=6,求△DEF的周长.
19-20八年级下·辽宁丹东·期末 查看更多[4]
辽宁省丹东市2019-2020学年八年级下学期期末数学试题浙江省温州市第二十一中学2020-2021学年八年级上学期第一次阶段测试数学试题辽宁省铁岭市2021-2022学年八年级下学期期中数学试题(已下线)开学收心考试模拟卷01-【微专题】2022-2023学年八年级数学下册常考点微专题提分精练(苏科版)
更新时间:2020-12-10 22:58:46
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【推荐1】如图,AB=AE,BD=EC,∠BCA=80º,求∠BDE的度数.
![](https://img.xkw.com/dksih/QBM/editorImg/2023/1/24/4ee35aa5-616d-4940-993b-19de1a382101.png?resizew=156)
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【推荐2】阅读并填空:两块完全相同的纸板
和
,按如图所示的方式叠放,阴影部分为重叠部分,点O为边
和
的交点试说明不重叠的两部分
与
全等的理由.
解:因为两三角形纸板完全相同(已知),
所以
,__________,__________(全等三角形对应边、对应角相等).
所以
__________(等式性质).
即
__________(等式性质).
完成以上说理过程.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
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解:因为两三角形纸板完全相同(已知),
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ec2c1f3a53a2c5bf175dc9093be83f7a.png)
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c9d07adcc6393baa078198a5ee750a6d.png)
即
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完成以上说理过程.
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【推荐3】小明同学遇到一个问题:
如图,
、
是矩形
的边
和
延长线上的两点,
与
相交于点
,且
,求证:
.小明想:可以证△ADQ和△ADE全等,根据全等三角形对应边相等可得DQ=DE,再证出△PCE和△EDA相似,根据相似三角形对应边成比例得到线段关系,进而可得
,易证
,然后根据
列式整理即可得证.下面展示的是这种方法的过程,请把内容补充完整.
![](https://img.xkw.com/dksih/QBM/2021/11/16/2852545574993920/2854489298591744/STEM/13833ed42e7e45fea8661d3ced8265b5.png?resizew=258)
证明:过点 E 作 EF//BC 交 AB 于 F.
由 ∠PAD=∠QAD,
易证△ADQ≌△ADE
∴DQ=DE,
∴
由∠DAE=∠EPC
易证△ADE∽△PCE
即____________________________
∵
,
如图,
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/acc290b44635265137fdf13146b6a6d9.png)
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证明:过点 E 作 EF//BC 交 AB 于 F.
由 ∠PAD=∠QAD,
易证△ADQ≌△ADE
∴DQ=DE,
∴
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/309ccec78a93e5577b723d9c3d866077.png)
由∠DAE=∠EPC
易证△ADE∽△PCE
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/627beb62d06d5c2a7d1c679889b18e64.png)
∵
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9e70e954b8e10b3f299633f255ff6085.png)
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【推荐2】如图,在
中,点
是
边的中点,点E在
上,点F在
延长线上,且
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【推荐1】如图,在△ABC中,
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【推荐2】如图,
内接于
,
是
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是
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作
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的延长线于点
,
平分
.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/10/5/247900e8-3e97-4e2d-a3f1-0807de8cc7b6.png?resizew=116)
(1)求证:
是
的切线;
(2)若
,
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(1)求证:
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