如图所示,在△ABC中,AB=AC,D是BC边上的点,DE⊥AB,DF⊥AC,垂足分别为点E、F,∠BAC=120°. 求证:
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/26bb1fb34413cca2d19642f694a7eff2.png)
![](https://img.xkw.com/dksih/QBM/2019/8/16/2270076167733248/2270246546317313/STEM/6d35783e4b744219a4f4d9cacebe8cf2.png?resizew=195)
更新时间:2019-08-16 22:11:20
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【推荐1】如图是A,B,C三个岛的平面图,C岛在A岛的北偏东32°方向,B岛在A岛的北偏东66°方向,C岛在B岛的北偏西44°方向.求C岛看A、B两岛的视角∠ACB的度数?
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【推荐2】如图,在
中,
,
,
的垂直平分线交
于点
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,
的垂直平分线交
于点
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【推荐1】课本再现∶
思考:
我们知道,矩形的对角线相等,反过来,对角线相等的平行四边形是矩形吗?
可以发现并证明矩形的一个判定定理:对角线相等的平行四边形是矩形
已知:在
中, 对角线 ![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7de966c316db1013defc56372fcf814e.png)
求证:四边形
是矩形
(2)如图2, 若点
为矩形
边
延长线上一点,且
平分
,
,若
,求
的长为多少?
思考:
我们知道,矩形的对角线相等,反过来,对角线相等的平行四边形是矩形吗?
可以发现并证明矩形的一个判定定理:对角线相等的平行四边形是矩形
已知:在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5138a9f70d5e8b0580e30fef6eb7baef.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7de966c316db1013defc56372fcf814e.png)
求证:四边形
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
(2)如图2, 若点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
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【推荐2】如图,
是
直径,
是
的弦,
,
(1)求
的度数.
(2)若
的半径
,求
的长.
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(1)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/246a86f34603eaf2e6a948681b831b0d.png)
(2)若
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【推荐1】已知:如图所示,E为正方形ABCD外一点,AE=AD,∠ADE=75°,求∠AEB的度数.
![](https://img.xkw.com/dksih/QBM/2016/7/28/1574221888208896/1574221894311936/STEM/ee804f46cec44012a3ab9fe625b1742f.png?resizew=126)
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【推荐2】如图,
是
的中线,且
,E为
上一点,连接
,且
.
![](https://img.xkw.com/dksih/QBM/editorImg/2023/12/14/bd94c971-3921-4f36-9491-1c7f2b05cb48.png?resizew=155)
(1)求证:
;
(2)若
,
,试求线段
的长.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0b1f8c020a6e3991537f7b634df041c0.png)
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(1)求证:
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(2)若
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