如图,菱形ABCD的对角线交于点O,点E是菱形外一点,DE
AC,CE
BD.
(1)求证:四边形DECO是矩形;
(2)连接AE交BD于点F,当∠ADB=30°,DE=2时,求AF的长度.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a9bfa68259d7a331be323b2038d628a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a9bfa68259d7a331be323b2038d628a.png)
(1)求证:四边形DECO是矩形;
(2)连接AE交BD于点F,当∠ADB=30°,DE=2时,求AF的长度.
![](https://img.xkw.com/dksih/QBM/2019/7/4/2239454099841024/2240250395254784/STEM/71582fbe595b494ab670b129e4ca796e.png?resizew=185)
更新时间:2019-07-05 13:04:00
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解答题-证明题
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【推荐1】如图,等腰△ABC中,已知AC=BC=
,AB=2,作∠ACB的外角平分线CF,点E从点B沿着射线BA以每秒1个单位的速度运动,过点E作BC的平行线交CF于点F.
(1)求证:四边形BCFE是平行四边形;
(2)当点E是边AB的中点时,连接AF,试判断四边形AECF的形状,并说明理由;
(3)设运动时间为t秒,是否存在t的值,使得以△EFC的其中两边为邻边所构造的平行四边形恰好是菱形?不存在的,试说明理由;存在的,请直接写出t的值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d4056761b8f826eeb6ad8c9a151d3c9c.png)
(1)求证:四边形BCFE是平行四边形;
(2)当点E是边AB的中点时,连接AF,试判断四边形AECF的形状,并说明理由;
(3)设运动时间为t秒,是否存在t的值,使得以△EFC的其中两边为邻边所构造的平行四边形恰好是菱形?不存在的,试说明理由;存在的,请直接写出t的值.
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解答题-证明题
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适中
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【推荐2】如图,在
中,
,
分别是
,
边上的点,
,连接
.
,
的平分线分别交
,
边于点
,
,连接
,
.
(1)求证:四边形
是平行四边形;
(2)小明在完成(1)的证明后继续探索,他猜想:当
为
的中点时,四边形
是矩形,请在下列框图中补全他的证明思路.
小明的证明思路
连接
.由(1)知四边形
是平行四边形.要证
是矩形,只要证
.
故只要证
.
由已知条件______,故只要证
,
即证四边形
为平行四边形.易证______
故只要证
,易证
,故只要证______, 易证
,即可得证.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5138a9f70d5e8b0580e30fef6eb7baef.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a0ed1ec316bc54c37c4286c208f55667.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/03902478df1a55bc99703210bccab910.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/86d1125b47dec1c5e93143ee59ad862a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/49b50357a6545cae8348e3059312f520.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b3909f220cf6bd065e382e263b77aa22.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d27bc78604ee7b6e013980b72686f9ca.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d78abbad68bbbf12af10cd40ef4c353.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac047e91852b91af639feec23a9598b2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/54a5d7d3b6b63fe5c24c3907b7a8eaa3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9ce6c0e9de83f2e64ae33609fc08459d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/360496a4f5cc8a5faca5e089ae4f9531.png)
(1)求证:四边形
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/05a270ec7e23fc0cc1d4b04bf1d22184.png)
(2)小明在完成(1)的证明后继续探索,他猜想:当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac047e91852b91af639feec23a9598b2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/05a270ec7e23fc0cc1d4b04bf1d22184.png)
小明的证明思路
连接
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411461db15ee8086332c531e086c40c7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/05a270ec7e23fc0cc1d4b04bf1d22184.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb36f828ad7d1f1359225b97a5117d8e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3f9bc3d52c7d01890b09ed152e4c8662.png)
故只要证
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3ee15c70230f88aa1b6e47a55d456530.png)
由已知条件______,故只要证
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0e3782593a403e59f30f5a657105b03d.png)
即证四边形
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b80a0e428cb894bfd09a6129a73ea4ac.png)
故只要证
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b8ff398bdaa4eb5a274f86c0d8b77ef2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0fc5f0e2cc2158bd508edd68e05a892b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/73d4caeab4058ff746569e52baf6485e.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/10/25/e814ae7c-17a7-4f20-9450-d06aea2f4181.png?resizew=208)
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【推荐1】如图,在菱形
中,
=60°, AB=2,点E是AB上的动点,作∠EDQ=60°交BC于点Q,点P在AD上,PD=PE.
(1)求证:AE=BQ;
(2)连接PQ, EQ,当∠PEQ=90°时,求
的值;
(3)当AE为何值时,△PEQ是等腰三角形.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/411b38a18046fea8e9fab1f9f9b80a5f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4189a0821a0ffab9dc171ecd279ba442.png)
(1)求证:AE=BQ;
(2)连接PQ, EQ,当∠PEQ=90°时,求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ba9e815c18ed0820f421a1196114bbea.png)
(3)当AE为何值时,△PEQ是等腰三角形.
![](https://img.xkw.com/dksih/QBM/2019/8/1/2259240799633408/2263478231408640/STEM/499c0aa026d74069a1fe4fcad4e25571.png?resizew=190)
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名校
【推荐2】如图,已知菱形
的对角线
、
相交于点
,过点
作
的平行线,过点
作
的平行线,两线交于点
.
![](https://img.xkw.com/dksih/QBM/2021/9/8/2803692575866880/2806703470772224/STEM/47d95fe9-dedf-484a-825c-1fb22347c612.png)
(1)求证:四边形
是矩形;
(2)若
,
,求四边形
的周长.
![](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/1dde8112e8eb968fd042418dd632759e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5db41a1f31d6baee7c69990811edb9f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d40b319212a7e7528b053e1c7097e966.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/60ef95894ceebaf236170e8832dcf7e3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://img.xkw.com/dksih/QBM/2021/9/8/2803692575866880/2806703470772224/STEM/47d95fe9-dedf-484a-825c-1fb22347c612.png)
(1)求证:四边形
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/99399ce175a0f5d0a7a6a82d81b6af7f.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/06201e4f55b78d8b30afb257d5a1b16b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/795e740cb57615d48c36b416d5b93a9c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/99399ce175a0f5d0a7a6a82d81b6af7f.png)
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【推荐1】如图,
是
的直径,
是
的弦,且
,垂足为E,连接
,过点B作
的切线,交
的延长线于点F.
;
(2)若点
是
的中点,且
,求线段
的长;
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3d97cdc586744d208b6f69c9813af977.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dc25c327679afb273fa7def519088c.png)
(2)若点
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b90e0f35eda1a729fed485f83da5ea9d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2fc28f622892dd18bbbac95d541acfe.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/274cf35acb4a1748d15c39d15a9bea7b.png)
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解答题-应用题
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【推荐2】图1是某浴室花洒实景图,图2是该花洒的侧面示意图.已知活动调节点B可以上下调整高度,离地面
的距离
.设花洒臂与墙面的夹角为α,假设水柱
垂直
直线喷射,某小朋友在离墙面距离
处淋浴.当
时,求小朋友的身高
.(参考数据:
,
)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9d78abbad68bbbf12af10cd40ef4c353.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/68a83fdd2ba72a2dba0b6b10bb3e06b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f52a58fbaf4fea03567e88a9f0f6e37e.png)
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![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4c894b7d6baa55c80c64e74748dad898.png)
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