如图,已知AB是⊙O的直径,C是⊙O上的一点,D是AB上的一点,DE⊥AB于D,DE交BC于F,且EF=EC.
![](https://img.xkw.com/dksih/QBM/2021/5/2/2712440039768064/2715225006972928/STEM/26095511-d231-420a-926c-5f0b4177a42b.png?resizew=165)
(1)求证:EC是⊙O的切线;
(2)求证:△OAC∽△ECF
(3)若BD=4,BC=8,圆的半径OB=5,求切线EC的长.
![](https://img.xkw.com/dksih/QBM/2021/5/2/2712440039768064/2715225006972928/STEM/26095511-d231-420a-926c-5f0b4177a42b.png?resizew=165)
(1)求证:EC是⊙O的切线;
(2)求证:△OAC∽△ECF
(3)若BD=4,BC=8,圆的半径OB=5,求切线EC的长.
2021·广西南宁·一模 查看更多[3]
更新时间:2021-05-06 14:42:19
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【推荐1】如图,AB为⊙O的直径,AC、BD分别与⊙O相切于点A、B,连接OC、OD,OC⊥OD.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/9/15/818faafa-6c23-4d18-aa28-b6771b21701b.png?resizew=251)
(1)如图1,求证:CD与⊙O相切;
(2)如图2,延长DO交⊙O于点E,连接CE,若
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![](https://img.xkw.com/dksih/QBM/editorImg/2022/9/15/818faafa-6c23-4d18-aa28-b6771b21701b.png?resizew=251)
(1)如图1,求证:CD与⊙O相切;
(2)如图2,延长DO交⊙O于点E,连接CE,若
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【推荐2】如图,从
上一点A引出弦
和切线
,连接
,若
,
,请仅用无刻度的直尺,分别在图1,图2中画出符合下列条件的直线
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(1)在图1中,画直线
;
(2)在图2中,画
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(2)在图2中,画
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【推荐1】(1)如图①,在四边形
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解答题-证明题
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【推荐2】【问题背景】(1)如图1,
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作
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【推荐3】对于两个相似三角形,如果沿周界按对应点顺序环绕的方向相同,那么称这两个三角形互为顺相似;如果沿周界按对应点顺序环绕的方向相反,那么称这两个三角形互为逆相似.例如,如图(1),△CDE∽△CAB,且沿周界CDEC与CABC环绕的方向(同为逆时针方向)相同,因此△CDE和△CAB互为顺相似;如图(2),△CDE∽△CBA,且沿周界CDEC与CBAC环绕的方向相反,因此△CDE和△CBA互为逆相似.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/7/4e09e543-547c-42e5-ba66-51992bc07942.png?resizew=468)
(1)根据以上材料填空:
①如图(3),AB∥CD,则△AOB∽△COD,它们互为 相似(填“顺”或“逆”,下同);
②如图(4),Rt△ABC中,∠ACB=90°,CD⊥AB于点D,则△ABC∽ ,它们互为 相似;
③如图(5),若∠DAB=∠EBC=90°,并且BD⊥CE于点F,则△ABD∽ ,它们互为 相似;
(2)如图(6),若△AOB∽△COD,指出图中另外的一对相似三角形并说明理由,同时指出它们互为顺相似还是互为逆相似;
(3)如图(7),在Rt△ABC中,∠C=90°,AC=20,BC=15,点P在△ABC的斜边上,且AP=16,过点P画直线截△ABC,使截得的一个三角形与△ABC相似,则满足的截线共有 条.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/7/4e09e543-547c-42e5-ba66-51992bc07942.png?resizew=468)
(1)根据以上材料填空:
①如图(3),AB∥CD,则△AOB∽△COD,它们互为 相似(填“顺”或“逆”,下同);
②如图(4),Rt△ABC中,∠ACB=90°,CD⊥AB于点D,则△ABC∽ ,它们互为 相似;
③如图(5),若∠DAB=∠EBC=90°,并且BD⊥CE于点F,则△ABD∽ ,它们互为 相似;
(2)如图(6),若△AOB∽△COD,指出图中另外的一对相似三角形并说明理由,同时指出它们互为顺相似还是互为逆相似;
(3)如图(7),在Rt△ABC中,∠C=90°,AC=20,BC=15,点P在△ABC的斜边上,且AP=16,过点P画直线截△ABC,使截得的一个三角形与△ABC相似,则满足的截线共有 条.
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解题方法
【推荐1】已知△ABC中,AB=AC,点D、H分别在边BC、AC上,BH与AD交于点E,∠BAC=∠BED.
(1)如图①,若∠BAC=60°,求证:BD=CH;
(2)如图②,连接EC,若BE=2AE,求证:∠BED=2∠DEC.
(3)在(2)的条件下,延长AE至点F,连接BF、CF,∠ABE+∠ACE+∠BFE=90°,∠BFC=90°,DE=
,求CH的长.
(1)如图①,若∠BAC=60°,求证:BD=CH;
(2)如图②,连接EC,若BE=2AE,求证:∠BED=2∠DEC.
(3)在(2)的条件下,延长AE至点F,连接BF、CF,∠ABE+∠ACE+∠BFE=90°,∠BFC=90°,DE=
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【推荐2】如图1,△ABC中,AB=AC,点D在BA的延长线上,点E在BC上,DE=DC,点F是DE与AC的交点,且DF=FE.
![](https://img.xkw.com/dksih/QBM/2015/6/23/1573852759703552/1573852765691904/STEM/bbae0a08c5f4444390387622e2f353ba.png)
(1)图1中是否存在与∠BDE相等的角?若存在,请找出,并加以证明,若不存在,说明理由;
(2)求证:BE=EC;
(3)若将“点D在BA的延长线上,点E在BC上”和“点F是DE与AC的交点,且DF=FE”分别改为“点D在AB上,点E在CB的延长线上”和“点F是ED的延长线与AC的交点,且DF=kFE”,其他条件不变(如图2).当AB=1,∠ABC=a时,求BE的长(用含k、a的式子表示).
![](https://img.xkw.com/dksih/QBM/2015/6/23/1573852759703552/1573852765691904/STEM/bbae0a08c5f4444390387622e2f353ba.png)
(1)图1中是否存在与∠BDE相等的角?若存在,请找出,并加以证明,若不存在,说明理由;
(2)求证:BE=EC;
(3)若将“点D在BA的延长线上,点E在BC上”和“点F是DE与AC的交点,且DF=FE”分别改为“点D在AB上,点E在CB的延长线上”和“点F是ED的延长线与AC的交点,且DF=kFE”,其他条件不变(如图2).当AB=1,∠ABC=a时,求BE的长(用含k、a的式子表示).
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