(1)如图1,AD是△ABC的中线,延长AD至点E,使ED=AD,连接CE.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/9/12/82678225-83ea-4660-8886-f06afba92390.png?resizew=285)
①证明△ABD≌△ECD;
②若AB=5,AC=3,设AD=x,可得x的取值范围是_______;
(2)如图2,在△ABC中,D是BC边上的中点,DE⊥DF,DE交AB于点E,DF交AC于点F,连接EF,求证:BE+CF>EF.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/9/12/82678225-83ea-4660-8886-f06afba92390.png?resizew=285)
①证明△ABD≌△ECD;
②若AB=5,AC=3,设AD=x,可得x的取值范围是_______;
(2)如图2,在△ABC中,D是BC边上的中点,DE⊥DF,DE交AB于点E,DF交AC于点F,连接EF,求证:BE+CF>EF.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/9/12/3e1a556d-f2e9-48e2-a395-b9065a960249.png?resizew=250)
21-22八年级上·江苏南京·阶段练习 查看更多[6]
江苏省南京市玄武区某校2021-2022学年八年级上学期国庆作业数学试题江苏镇江句容市华阳片区2022-2023学年八年级上学期第一次月考数学试题江苏省镇江市句容市部分学校2022-2023学年八年级上学期10月月考数学试卷(已下线)专题05 全等三角形证明方法:倍长中线【考点串讲+热点题型专训】-2022-2023学年七年级数学下学期期中期末考点大串讲(北师大版)(已下线)重难点02全等三角形中“倍长中线”模型-【暑假自学课】2023年新八年级数学暑假精品课(苏科版)(已下线)12.3(培优课)倍长中线(题型精讲精练)-【题型分类精粹】2023-2024学年八年级数学上学期期中期末复习讲练系列【考点闯关】(人教版)
更新时间:2022-09-11 16:08:38
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【推荐1】用一条24cm的细绳围成一个等腰三角形.
(1)如果腰长是底边的2倍,那么各边的长是多少?
(2)能围成有一边长为4cm的等腰三角形吗?为什么?
(1)如果腰长是底边的2倍,那么各边的长是多少?
(2)能围成有一边长为4cm的等腰三角形吗?为什么?
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【推荐2】等腰三角形一腰上的中线将这个等腰三角形的周长分成12cm和9cm两部分,求等腰三角形的底边长.
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【推荐1】如图,已知
,
是线段
上的两点,
,
,
.以
为圆心,
的长为半径作圆弧;以
为圆心,
的长为半径作圆弧,两圆弧相交于点
,连接
,
,构成
,设
.
(1)求
的取值范围.
(2)若
为直角三角形,求
的值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411461db15ee8086332c531e086c40c7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20ee7af832af9460f4775fa5c8c3620f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ca7f2c76e2d7aafeafbba1f7d740850e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fc2fee2e2af167e84126fe551316fbe0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d50703c46b6153945d718b198f03b4b5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7785afeeaf274892253d04b4f693b367.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5db41a1f31d6baee7c69990811edb9f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8c7a3d679b4dae63575903387a76ce45.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/11/21/8b6319d5-ba84-455d-87c1-10365cacf8a2.png?resizew=195)
(1)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
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【推荐2】课外兴趣小组活动时,老师提出了下面问题:
如图①,
是
的中线,若
,
,求
的取值范围.
“善思小组”通过探究发现,延长
至点E,使
,连接
,可以证出
,利用全等三角形的性质,可将已知的边长与
转化到
中,进而求出
的取值范围.
从上面的思路可以看出,解决问题的关键是将中线
延长一倍,构造出全等三角形,我们把这种方法叫做“倍长中线法”.
请你利用“善思小组”的方法思考:
![](https://img.xkw.com/dksih/QBM/editorImg/2023/12/10/51bff4bc-5122-4c2a-a763-78f2dccfca6b.png?resizew=312)
(1)由已知和作图能得到
的理由是 ;
A.
B.
C.
D.
(2)求得
的取值范围是 ;
A.
B.
C.
D.
解题时,条件中若出现“中点”或“中线”字样,可以考虑延长中线构造全等三角形,把分散的已知条件和所求证的结论集合到同一三角形中.
根据上面解题方法的启发,请你解答问题.
(3)如图②,在
中,
,点D,E在
上,点E是
的中点,
交
于点F,
.求证:
平分
.
如图①,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/efc6e4b936d7a800e839a30c3839574d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c3ad4c0ba3a6750537789844d0ec419d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
“善思小组”通过探究发现,延长
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4abcd9292846e104dc2234b0aea41a81.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4eedae8d316c76e3d0b451256de03fb9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c7ddf7269f728a37a94b4ba714726307.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dcb49df05f2e31d005735c3f14a21d30.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
从上面的思路可以看出,解决问题的关键是将中线
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
请你利用“善思小组”的方法思考:
![](https://img.xkw.com/dksih/QBM/editorImg/2023/12/10/51bff4bc-5122-4c2a-a763-78f2dccfca6b.png?resizew=312)
(1)由已知和作图能得到
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c7ddf7269f728a37a94b4ba714726307.png)
A.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6720e36b02193db161c61d4017673760.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9beb8b968744573e593ac28451c69729.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d5eb2decaa6be2df36a5e4b7fabf585d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5a290f047f50481318d040c604d72f7.png)
(2)求得
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
A.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9735cbfb83fcc83bcfb0ed1b2c6d9006.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8a63e7421696dc670bd36d4557fb665a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/73dea81ca7038a96c566b95c21033191.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a109fc1776d69db84d20782ff27b9c73.png)
解题时,条件中若出现“中点”或“中线”字样,可以考虑延长中线构造全等三角形,把分散的已知条件和所求证的结论集合到同一三角形中.
根据上面解题方法的启发,请你解答问题.
(3)如图②,在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/abcb980da8e86b4cfd322616dc84fc6e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d78abbad68bbbf12af10cd40ef4c353.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/100b3e7dcd5f34c5234971cd75bff138.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f3ba14572ca99b865bdbecf3bbc788c0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7cbce11aa19b8bd2bf6ee5a834e005de.png)
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【推荐3】【阅读理解】课外兴趣小组活动时,老师提出了如下问题:
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/22/b46d864e-7058-4b77-aa73-439941c6811c.png?resizew=213)
如图1,
中,若
,
,求
边上的中线
的取值范围. 小明在组内经过合作交流,得到了如下的解决方法:延长
到点
,使
,请根据小明的方法思考:
(1)由已知和作图能得到
的理由请选择_________
A.
B.
C.
D. ![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eaff0dae15a94c9f2865c660ea44ce5f.png)
(2)AD的取值范围是_________.
(3)【感悟】解题时,条件中若出现“中点”“中线”字样,可以考虑延长中线构造全等三角形,把分散的已知条件和所求证的结论集中到同一个三角形中.
【问题解决】如图2,
是
的中线,
交
于点
,交
于点
,且
,求证:
![](https://img.xkw.com/dksih/QBM/editorImg/2022/11/22/b46d864e-7058-4b77-aa73-439941c6811c.png?resizew=213)
如图1,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9f08273d339dc5ddbb89aa67bb8205e6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a8a7b5adfcac0f46a4cd19da4ebb4a2b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0ad98ad714864041a632ca949308e417.png)
(1)由已知和作图能得到
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ab24c24cef4dd5162753308a6631cb01.png)
A.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3ef21f6c326b310efdc1bc2f377b2fc9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9730d8c39620a403e38171c723d3dfea.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4194089bef4e0d583fc1e69f0e235ae5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eaff0dae15a94c9f2865c660ea44ce5f.png)
(2)AD的取值范围是_________.
(3)【感悟】解题时,条件中若出现“中点”“中线”字样,可以考虑延长中线构造全等三角形,把分散的已知条件和所求证的结论集中到同一个三角形中.
【问题解决】如图2,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/85c4bdfb0db1e31e8459df1d15f9ab55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a0ed1ec316bc54c37c4286c208f55667.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3767efa8adfb71001ad39df9560cbf6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a5787c784b686435a2073bdeb836307c.png)
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解题方法
【推荐2】如图1,
的边
在直线
上,
,且
;
的边
也在直线
上,边
与边
重合,且
.
![](https://img.xkw.com/dksih/QBM/2020/11/24/2599992222892032/2609081157771264/STEM/b402634c-2565-4e7a-8a4d-ea394596e8a5.png?resizew=720)
(1)示例:在图1中,通过观察、测量,猜想并写出
与
所满足的数量关系和位置关系.
答:
与
的数量关系和位置关系分别是_________、_________.
(2)将
沿直线
向左平移到图2的位置时,
交
于点
,
,连结
,
.请你观察、测量,猜想并写出
与
所满足的数量关系和位置关系.
答:
与
的数量关系和位置关系分别是_________、_________.
(3)将
沿直线
向左平移到图3的位置时,
的延长线交
的延长线于点
,
,连结
、
.你认为(2)中所猜想的
与
的数量关系和位置关系还成立吗?若成立,给出证明;若不成立,请说明理由.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0faed94a64b2dcfc6801b4fca0f16675.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f85fca60a11e1af2bf50138d0e3fe62.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/615fc8790237a1b09af51d6bcad6b595.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4b10134e7a46e6f6f7cb9d5e2371727d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8757662c6bf052bcd553ffac5672d802.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b5c2293f93791a597bf0162411f3395f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f85fca60a11e1af2bf50138d0e3fe62.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/49b50357a6545cae8348e3059312f520.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/996921128e41ae0449bd0ba22b08a219.png)
![](https://img.xkw.com/dksih/QBM/2020/11/24/2599992222892032/2609081157771264/STEM/b402634c-2565-4e7a-8a4d-ea394596e8a5.png?resizew=720)
(1)示例:在图1中,通过观察、测量,猜想并写出
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
答:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
(2)将
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8757662c6bf052bcd553ffac5672d802.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f85fca60a11e1af2bf50138d0e3fe62.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4f541f7ae7c39082d202efd28805c54e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/acc290b44635265137fdf13146b6a6d9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7210c2fbdb84b991377bf492e29cd8a9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb6ede9761b5b90f8dc137708e1ee90f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb6ede9761b5b90f8dc137708e1ee90f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
答:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb6ede9761b5b90f8dc137708e1ee90f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
(3)将
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8757662c6bf052bcd553ffac5672d802.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f85fca60a11e1af2bf50138d0e3fe62.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4f541f7ae7c39082d202efd28805c54e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/acc290b44635265137fdf13146b6a6d9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7210c2fbdb84b991377bf492e29cd8a9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb6ede9761b5b90f8dc137708e1ee90f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb6ede9761b5b90f8dc137708e1ee90f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/20a541b81584a032f571159ea152c85a.png)
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