数学概念:如图①,在△ABC中,D为∠ABC的对边AC上一点(点D不与点A、C重合),连接BD.若∠ADB和∠CDB这两个角中至少存在1个与∠ABC相等,则称BD为△ABC中∠ABC的等角分割线.
![](https://img.xkw.com/dksih/QBM/2022/3/18/2938909935804416/2941001725878272/STEM/70c78f2ff538489e8f3e9874cf1e1362.png?resizew=268)
(1)概念理解:如图②,在Rt△ABC中,∠C=90°,∠B=60°.分别画出∠B和∠C的等角分割线BD、CE.(画图工具不限,并做出适当的标注)
(2)知识运用:在△ABC中,∠A=45°,∠ACB=75°.已知∠ABC、∠ACB的等角分割线BD、CE相交于点O,求∠BOC的度数.
(3)深入思考:下列关于“等角分割线”的结论:
①钝角三角形中的钝角有2条等角分割线;
②任意一个三角形中最少有1条等角分割线,最多有3条等角分割线.
③三角形的高、角平分线可能是该三角形中的等角分割线;
④三个角都不相等的三角形中,最小的角没有等角分割线;
其中所有正确结论的序号是 .
![](https://img.xkw.com/dksih/QBM/2022/3/18/2938909935804416/2941001725878272/STEM/70c78f2ff538489e8f3e9874cf1e1362.png?resizew=268)
(1)概念理解:如图②,在Rt△ABC中,∠C=90°,∠B=60°.分别画出∠B和∠C的等角分割线BD、CE.(画图工具不限,并做出适当的标注)
(2)知识运用:在△ABC中,∠A=45°,∠ACB=75°.已知∠ABC、∠ACB的等角分割线BD、CE相交于点O,求∠BOC的度数.
(3)深入思考:下列关于“等角分割线”的结论:
①钝角三角形中的钝角有2条等角分割线;
②任意一个三角形中最少有1条等角分割线,最多有3条等角分割线.
③三角形的高、角平分线可能是该三角形中的等角分割线;
④三个角都不相等的三角形中,最小的角没有等角分割线;
其中所有正确结论的序号是 .
更新时间:2022-03-21 14:26:14
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【推荐1】(1)如图①∠1+∠2与∠B+∠C有什么关系?为什么?
(2)把图①△ABC沿DE折叠,得到图②,填空:
∠1+∠2 ∠B+∠C(填“>”“<”“=”),当∠A=60°时,∠B+∠C+∠1+∠2=
(3)如图③,是由图①的△ABC沿DE折叠得到的,猜想∠BDA+∠CEA与∠A的关系,并证明你的猜想.
(2)把图①△ABC沿DE折叠,得到图②,填空:
∠1+∠2 ∠B+∠C(填“>”“<”“=”),当∠A=60°时,∠B+∠C+∠1+∠2=
(3)如图③,是由图①的△ABC沿DE折叠得到的,猜想∠BDA+∠CEA与∠A的关系,并证明你的猜想.
![](https://img.xkw.com/dksih/QBM/2019/10/7/2306987366752256/2309150933483520/STEM/e9cd2c5aef4c4bb5a089eb529923afdf.png?resizew=457)
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【推荐2】平面内的不重合的两条直线有相交和平行两种位置关系.
,点
在
内部,
,
.
(2)如图2,若
,将点
移到
外部,则
之间有何数量关系?请证明你的结论.
(3)如图3,直接写出
之间的数量关系
(4)拓展:已知
,在
之间取一点
(点
不在直线
上),连接
,若
的平分线
交于点M,试探索
与
之间的数量关系(直接写出结果)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b0fff774b4b0087a6f304ce930d359be.png)
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(2)如图2,若
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(3)如图3,直接写出
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f8df10ec0440fdc0deac059f03e3c907.png)
(4)拓展:已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b0fff774b4b0087a6f304ce930d359be.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c28d2790a97390935125aa897417f970.png)
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【推荐1】如图,E在
上,
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的中点.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/12/28/abb47c82-f759-48bd-9f3d-eca6d18e922f.png?resizew=172)
(1)求证:
;
(2)
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(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4b6cc3789c0e9b7d1226aa0de3327599.png)
(2)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/df49f1e9f4c7abe07c0e238e982b0f94.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/32436704a722d5e568ff5c175bf3c662.png)
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【推荐2】【生活常识】射到平面镜上的光线(入射光线)和变向后的光线(反射光线)与平面镜所夹的角相等,如图1,
是平面镜,若入射光线
与水平镜面夹角为
,反射光线
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【应用探究】有两块平面镜
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与
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【应用探究】有两块平面镜
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/235a46f917a962ab23ca558a9a957aa0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0c4c3c0a34dc21292fa32befd58d8f82.png)
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