在
中,E、F分别是边BC,AD的中点,AC是对角线,过点D作DP
AC,交BA的延长线于点P,∠P=90°.求证:四边形AECF是菱形.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7eacc7b8ce618cc923acd65e9fb7b424.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f623667ca9e6ed42bb03431116992f71.png)
![](https://img.xkw.com/dksih/QBM/2022/10/13/3086754081882112/3090929676165120/STEM/9041930896344244873aae87e933c2da.png?resizew=178)
更新时间:2022-10-19 10:15:26
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【推荐1】 问题与探索
问题情境:课堂上,老师让同学们以“菱形纸片的剪拼”为主题开展数学活动.如图(1),将一张菱形纸片ABCD(∠BAD>90°)沿对角线AC剪开,得到△ABC和△ACD.
操作发现:
(1)将图(1)中的△ACD以点A为旋转中心,按逆时针方向旋转角α,使α=∠BAC,得到如图(2)所示的△AC′D,分别延长BC和DC′交于点E,则四边形ACEC′的形状是 .
(2)创新小组将图(1)中的△ACD以点A为旋转中心,按逆时针方向旋转角α,使α=2∠BAC,得到如图(3)所示的△AC′D,连接DB、C′C,得到四边形BCC′D,发现它是矩形,请证明这个结论.
问题情境:课堂上,老师让同学们以“菱形纸片的剪拼”为主题开展数学活动.如图(1),将一张菱形纸片ABCD(∠BAD>90°)沿对角线AC剪开,得到△ABC和△ACD.
操作发现:
(1)将图(1)中的△ACD以点A为旋转中心,按逆时针方向旋转角α,使α=∠BAC,得到如图(2)所示的△AC′D,分别延长BC和DC′交于点E,则四边形ACEC′的形状是 .
(2)创新小组将图(1)中的△ACD以点A为旋转中心,按逆时针方向旋转角α,使α=2∠BAC,得到如图(3)所示的△AC′D,连接DB、C′C,得到四边形BCC′D,发现它是矩形,请证明这个结论.
![](https://img.xkw.com/dksih/QBM/2016/12/14/1633712098140160/1633712098500608/STEM/033da5664c334b24a6a00785439ed6c5.png)
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【推荐2】阅读下面材料,并回答问题
在几何学习中,经常通过添加辅助线构造图形,将未知问题转化为已知问题.以下给出的“三角形中位线定理”的两种不同证明方法,就体现了三角形问题和平行四边形问题的相互转化.
在几何学习中,经常通过添加辅助线构造图形,将未知问题转化为已知问题.以下给出的“三角形中位线定理”的两种不同证明方法,就体现了三角形问题和平行四边形问题的相互转化.
方法一 已知:如图①,在 ![]() ![]() ![]() ![]() ![]() ![]() 求证: ![]() ![]()
证明:延长 ![]() ![]() ![]() 连接 ![]() ![]() ![]() ∵ ![]() ![]() ∴四边形 ![]() ∴ ![]() ∵ ![]() ∴ ![]() ∴四边形 ![]() ∴ ![]() ![]() 又 ![]() ∴ ![]() ![]() | 方法二 已知:如图②,在 ![]() ![]() ![]() ![]() ![]() ![]() 求证: ![]() ![]()
证明:过点 ![]() ![]() ![]() ![]() ∴ ![]() ∵ ![]() ![]() ∴ ![]() ∴ ![]() 又 ![]() ∴ ![]() ∴四边形 ![]() ∴ ![]() 又 ![]() ∴ ![]() ![]() |
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解答题-问答题
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【推荐1】如图,在
中,
,点
是线段
上一动点,连结
.
![](https://img.xkw.com/dksih/QBM/editorImg/2024/2/22/34d3a07d-3fe7-4f46-8176-00cc5a1ed11c.png?resizew=582)
(1)当
为等腰三角形时,直接写出
的度数.
(2)当点
是
的中点时,求
的度数.
(3)过点
作
,垂足分别点
,求连结
,求
的最小值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ff21fb84a5f22591686121ac474fbfa0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2024/2/22/34d3a07d-3fe7-4f46-8176-00cc5a1ed11c.png?resizew=582)
(1)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ab2a2834d80ff574e79eae8ca8d4e94f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/721c75fcd58d3d54260aad0f82e09e37.png)
(2)当点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/721c75fcd58d3d54260aad0f82e09e37.png)
(3)过点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dada4b823d9b13e0dd3cb1e029526cd8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ad056c25c0fdcbcc765eb5cbc6093f2b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/49b50357a6545cae8348e3059312f520.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/49b50357a6545cae8348e3059312f520.png)
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【推荐2】已知锐角△ABC中,CD,BE分别是AB,AC边上的高,M是线段BC的中点,连接DM,EM.
(1) 若DE=3,BC=8,求△DME的周长;
(2) 若∠A=60°,求证:∠DME=60°;
(3) 若BC2=2DE2,求∠A的度数.
(1) 若DE=3,BC=8,求△DME的周长;
(2) 若∠A=60°,求证:∠DME=60°;
(3) 若BC2=2DE2,求∠A的度数.
![](https://img.xkw.com/dksih/QBM/2019/1/5/2112124018655232/2113466320224256/STEM/68e847412aa24f11bd261bb096b89eab.png?resizew=202)
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【推荐1】阅读下面材料,并完成相应的任务.
三等分角是古希腊三大几何问题之一.如图,任意
可被看作是矩形
的对角线
与边
的夹角,以点
为端点的射线
交
于点
,交
的延长线于点
.若
,则
是
的一个三等分角.
的中点
,连接
.
∵四边形
是矩形,∴
,
.∴
.
在
中,∵点
是
的中点,∴
,
,
.
……
任务一:上而证明过程中得出“
”的依据是______;
任务二:完成材料证明中的剩余部分.
三等分角是古希腊三大几何问题之一.如图,任意
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d39b8d91afc34e4a9b0fdbb6bafb9087.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9c593ebdb2f1934a0cb56f8c44f454f8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7dea2ae9d515f9ab351ad72306b776ee.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/274cf35acb4a1748d15c39d15a9bea7b.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/67d822262ff00915910e5b87d81ad1ba.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a0ed1ec316bc54c37c4286c208f55667.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9366db1b71034abbe1a5693689cf1c22.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5d59511c474942171fb685fc3f8dfd2d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d39b8d91afc34e4a9b0fdbb6bafb9087.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/49b50357a6545cae8348e3059312f520.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/895dc3dc3a6606ff487a4c4863e18509.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/77a7e4a6765ce78b05ee97764771e01f.png)
∵四边形
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9c593ebdb2f1934a0cb56f8c44f454f8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b922c7fc50a56933a6cb9d80b1e7bb6c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4adf90a8c2b29334cdc5aa5b554991f9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5abd9251169862419818402ef6178b9a.png)
在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c922cbd707131b52757c464804ca24f1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/895dc3dc3a6606ff487a4c4863e18509.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/49b50357a6545cae8348e3059312f520.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/78917334e28fb7dbf45f7dceb80f05a0.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/64d5dd28658b689bdc7df601f179fd2f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2b81df15c5023b05e170cab718777105.png)
……
任务一:上而证明过程中得出“
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/78917334e28fb7dbf45f7dceb80f05a0.png)
任务二:完成材料证明中的剩余部分.
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【推荐2】如图,四边形ABCD是平行四边形,AC和BD相交于点O,过点O作AC的垂线分别交AD,BC于点E,点F,连接AF,CE.
(2)若
,
,求四边形AFCE的周长.
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/377786f0bb21bd9f009b513b3673d97f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9f08273d339dc5ddbb89aa67bb8205e6.png)
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【推荐1】如图,
中,
,
,
为
的中线,作
于
,点
在
延长线上,
,连接
、
.
求证:四边形
为菱形;
把
分割成三个全等的三角形,需要两条分割线段,若
,求两条分割线段长度的和.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e428e7a09732be85c1224e9c8f6a71c5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b82862a3ea06d5c719ac26406d19f4ca.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/19381fa72acd3baaed536b28703fd9fb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e1ffb98f1e3c1317c0db403d3af04bdc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e428e7a09732be85c1224e9c8f6a71c5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a78411ded00e4758b7963832aa4fada3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b1a3eb9576531c4ca1077be7cb5ef14b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e491964b08c1ab19a71bc1b04dfe2b3e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d0213c5787a5a6b38d11bceca5567f67.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1a6c6e7c025362c46a64a8956761f08e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/33b826293fd7cf6dc42bfc221346e6b2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/077956e5f55232814d1a077af264590e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/65863c1abad833b79c303bfca24f535c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e428e7a09732be85c1224e9c8f6a71c5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6ddeb9efb488b31ae67efd29efd56b3f.png)
![](https://img.xkw.com/dksih/QBM/2018/9/29/2042731640496128/2044156610256896/STEM/7ec7d2d553194e0ba68f77a6da8fb103.png?resizew=226)
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【推荐2】在数学课上,老师请同学们思考如下问题:如图①,我们把一个四边形
的四边中点依次连接起来,得到的四边形
是平行四边形吗?小敏在思考问题时,有如下思路:如图①,连接
.∵E,F分别是
,
的中点,∴
,
.∵G,H分别是
,
的中点,∴
,
.∴
,
.∴四边形
是平行四边形.
(1)若只改变图①中四边形
的形状(如图②),连接
,
,则四边形
还是平行四边形吗?请说明理由(参考小敏思考问题的方法解决).
(2)如图②,在(1)的条件下:
①当
与
满足什么条件时,四边形
是菱形?写出结论并证明.
②当
与
满足什么条件时,四边形
是矩形?直接写出结论.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/611f100dcfa7803db6eb233e2e7f2dab.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fedf634c305704c1c13cb0353d5dc7c5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9c62cca87325b32db22204f7cfa6cbb2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d78abbad68bbbf12af10cd40ef4c353.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bbe2c8281ad3442a26ea9d556b888089.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a9696901d0c3ecba9f1181dad381127e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d5188eea602f0d1a5a08da3fc421a076.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ddeac29a796a890dac3c4cc58de07ac7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/611f100dcfa7803db6eb233e2e7f2dab.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2023/5/23/2f9e209d-eb04-4045-b9e8-e0660f8708f8.png?resizew=354)
(1)若只改变图①中四边形
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d40b319212a7e7528b053e1c7097e966.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/611f100dcfa7803db6eb233e2e7f2dab.png)
(2)如图②,在(1)的条件下:
①当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d40b319212a7e7528b053e1c7097e966.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/611f100dcfa7803db6eb233e2e7f2dab.png)
②当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d40b319212a7e7528b053e1c7097e966.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/611f100dcfa7803db6eb233e2e7f2dab.png)
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