如图,在四边形ABCD中,AD∥BC,AD=BC=2AB,F是AD的中点,作CE⊥AB,垂足E在线段AB上,连接EF、CF.
(1)若∠ADC=80°,求∠ECF;
(2)求证:∠ECF=∠CEF.
(1)若∠ADC=80°,求∠ECF;
(2)求证:∠ECF=∠CEF.
![](https://img.xkw.com/dksih/QBM/2020/3/24/2426279150239744/2427421589897216/STEM/27e459060adc486f99c141179c5dd0d5.png?resizew=179)
19-20九年级下·安徽合肥·阶段练习 查看更多[4]
2020年安徽省合肥四十六中南校区3月中考模拟数学试题2020年山东省泰安市岱岳区九年级中考三模数学试题(已下线)【万唯原创】2021年安徽省试题研究-题组-基础解答题题组特训3山东省枣庄市峄城区山东枣庄东方国际学校2022-2023学年八年级下学期第二次质量检测数学试题
更新时间:2020-03-25 23:44:46
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解答题-问答题
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【推荐1】(1)【操作发现】
如图1,在边长为1个单位长度的小正方形组成的网格中,△ABC的三个顶点均在格点上.
①按要求画图:将△ABC绕点A顺时针方向旋转90°,点B的对应点为点B′,点C的对应点为点C′.连接BB′;
②在①中所画图形中,∠AB′B= .
(2)【问题解决】
如图2,在RtABC中,BC=1,∠C=90°,延长CA到D,使CD=1,将斜边AB绕点A顺时针旋转90°到AE,连接DE,求∠ADE的度数.
![](https://img.xkw.com/dksih/QBM/2021/8/2/2777600933707776/2784487542136832/STEM/1e7b1c91-22ec-4f05-b592-0ab5e9d214d5.png)
如图1,在边长为1个单位长度的小正方形组成的网格中,△ABC的三个顶点均在格点上.
①按要求画图:将△ABC绕点A顺时针方向旋转90°,点B的对应点为点B′,点C的对应点为点C′.连接BB′;
②在①中所画图形中,∠AB′B= .
(2)【问题解决】
如图2,在RtABC中,BC=1,∠C=90°,延长CA到D,使CD=1,将斜边AB绕点A顺时针旋转90°到AE,连接DE,求∠ADE的度数.
![](https://img.xkw.com/dksih/QBM/2021/8/2/2777600933707776/2784487542136832/STEM/1e7b1c91-22ec-4f05-b592-0ab5e9d214d5.png)
![](https://img.xkw.com/dksih/QBM/2021/8/2/2777600933707776/2784487542136832/STEM/9083b6a5-e26d-40d2-a0c1-1b78042b26c8.png)
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【推荐2】如图,在△ABC中,AB=AC,CD⊥AB于点D,CE为△ACD的角平分线,EF⊥BC于点F,EF交CD于点G,求证:BE=CG.
![](https://img.xkw.com/dksih/QBM/2015/2/4/1573793238482944/1573793244807168/STEM/9fa41cb5693641089192b7a809fb96d8.png)
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名校
【推荐1】如图,已知在
中,
,
,
是
边上的中线,点
,
分别在
和
上,
,
于点
.
;
(2)若
平分
,其余条件不变,求证:
.
(先将图形补充完整,然后再证明)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dd967903ed5a6f640a5b801ec8be0070.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/45acdbac251ca6b76a166c1242e71df9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3570a95f68349fcd9417fcda62e78e7e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aaf1438142deeac876fc7dc50552e552.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dad2a36927223bd70f426ba06aea4b45.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2c3d2cba96f6f03520c0b3f6e4da03e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/32d0710321d97361e5782124bbf7f0c9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68fbbd17c89f03dbb61cd6ffdb9a0344.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0bb1fbbc431abd3ce63a0ff979e39030.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d2be49c37e30a3ced0364c3e74d8c687.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d2bc29145f6e7557711c34b443bd5e84.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08ad2563f18f321e5fcf4a9f5ba1fd26.png)
(先将图形补充完整,然后再证明)
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解答题-作图题
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【推荐2】北师大九年级下册课本中有这样一个问题:已知
外一点
,你能用尺规过点
作
的切线吗?数学小组在课堂上对这个问题展开探究,大家提出了不同的方法,汇总如下:
小红提出:
(1)连接
并延长,分别交
于点
,
;
(2)以点
为圆心,
的长为半径画弧;
(3)以点
为圆心,
的长为半径画弧,两弧交于点
;
(4)连接
,交
于点
;
(5)连接
,则
即为所求.
小明提出:
(1)连接
并延长到点
,使
;
(2)以点
为圆心,以
的直径长为半径画弧;
(3)以点
为圆心,
的长为半径画弧,交(2)中所画弧于点
;
(4)连接
,则
即为所求.
请你任意选择一种方法在如下图中用无刻度的直尺和圆规过点
作
的切线(要求:不写作法,保留作图痕迹,使用2B铅笔作图),并说明该方法成立的理由.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3d97cdc586744d208b6f69c9813af977.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3d97cdc586744d208b6f69c9813af977.png)
小红提出:
(1)连接
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2c3d2cba96f6f03520c0b3f6e4da03e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3d97cdc586744d208b6f69c9813af977.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5db41a1f31d6baee7c69990811edb9f.png)
(2)以点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
(3)以点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2c3d2cba96f6f03520c0b3f6e4da03e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
(4)连接
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/683c590673eece14fea3319c4fd5eb55.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3d97cdc586744d208b6f69c9813af977.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
(5)连接
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
小明提出:
(1)连接
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2c3d2cba96f6f03520c0b3f6e4da03e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f4564bc6a257646a6ba4f281f31f4942.png)
(2)以点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3d97cdc586744d208b6f69c9813af977.png)
(3)以点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ef4113c492885ba7c47fe42ac792578f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
(4)连接
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
请你任意选择一种方法在如下图中用无刻度的直尺和圆规过点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3d97cdc586744d208b6f69c9813af977.png)
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【推荐1】 如图,等腰梯形ABCD中,AD∥BC,点E是线段AD上的一个动点(E与A、D不重合),G、F、H分别是BE、BC、CE的中点.
![](https://img.xkw.com/dksih/QBM/2013/1/24/1573597191168000/1573597217464320/STEM/4926e0e80b044f3bb2bca7a3c975bbf4.png)
(1)试探索四边形EGFH的形状,并说明理由;
(2)当点E运动到什么位置时,四边形EGFH是菱形?并说明理由;
(3)若(2)中的菱形EGFH是正方形,请探索线段EF与线段BC的关系,并说明你的理由.
![](https://img.xkw.com/dksih/QBM/2013/1/24/1573597191168000/1573597217464320/STEM/4926e0e80b044f3bb2bca7a3c975bbf4.png)
(1)试探索四边形EGFH的形状,并说明理由;
(2)当点E运动到什么位置时,四边形EGFH是菱形?并说明理由;
(3)若(2)中的菱形EGFH是正方形,请探索线段EF与线段BC的关系,并说明你的理由.
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解答题-证明题
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【推荐2】如图,在四边形
中,
,
,
,点
是边
的中点,连接
并延长与
的延长线交于点
,连接
、
.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/8/31/c7b8b84f-5de2-4261-a03c-bfd7ccea5afd.png?resizew=146)
(1)求证:四边形
是平行四边形;
(2)若
,求
的长.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7af7f3ef883a66428798c0665810ec71.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3f4aca5534bce25acaeb7379deed8f8f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3f8eeeea1c9652cacce976f8129cf520.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d78abbad68bbbf12af10cd40ef4c353.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/85c4bdfb0db1e31e8459df1d15f9ab55.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/4cae70b8a9d2d2e96dea62c00ced04b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d40b319212a7e7528b053e1c7097e966.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/8/31/c7b8b84f-5de2-4261-a03c-bfd7ccea5afd.png?resizew=146)
(1)求证:四边形
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/10af0a2e32fb3f3af9664617ac05b669.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/feb67f27bcda7681b19239a199b4c4d1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/274cf35acb4a1748d15c39d15a9bea7b.png)
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