名校
1 . 下列命题正确的有:________ .
①
;
②已知
,若
,则
.
③用反证法证明“已知
,且
,求证:
.”时,应假设“
且
”;
④命题“若
,则
”的逆否命题是“若
,则
”.
①
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/88d06a4bdf067ee8c14ce02d71271ddf.png)
②已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2dcbca3478eae63853d2aab5332e2e56.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eecb11de93939d81b65541b0bbdeb7f7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8efd32ba5030535598e979fd6d3a4d5c.png)
③用反证法证明“已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2dcbca3478eae63853d2aab5332e2e56.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c988d709ba8cd8aed6cb83d76c0ba89c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ea5977232839b54df456aeeacb13512d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/38f0e9c04402a0ffdaa25c3e3c82c7dd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1c412d5329ba909164329663b7eecdfe.png)
④命题“若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d1fdf7d28b97fb6fe731703f80e122ed.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9b384412acba251d87902ab928902f16.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0e30c903d8f8a05332af0b19e7e40df3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9a8a2a94168af9b16ce89271a5d8dc6b.png)
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2021高二下·全国·专题练习
2 . 完成反证法证题的全过程.
题目:设a1,a2,
,a7是由数字1,2,
,7任意排成的一个数列.
求证:乘积p=(a1-1)(a2-2)
(a7-7)为偶数.
证明:假设p为奇数,则________ 均为奇数.①
因为7个奇数之和为奇数,故有
(a1-1)+(a2-2)+
+(a7-7)为________ .②
而(a1-1)+(a2-2)+
+(a7-7)
=(a1+a2+
+a7)-(1+2+
+7)=________ .③
②与③矛盾,故p为偶数.
题目:设a1,a2,
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daa5e9bd516f6282483b92cfe6074623.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daa5e9bd516f6282483b92cfe6074623.png)
求证:乘积p=(a1-1)(a2-2)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daa5e9bd516f6282483b92cfe6074623.png)
证明:假设p为奇数,则
因为7个奇数之和为奇数,故有
(a1-1)+(a2-2)+
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daa5e9bd516f6282483b92cfe6074623.png)
而(a1-1)+(a2-2)+
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daa5e9bd516f6282483b92cfe6074623.png)
=(a1+a2+
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daa5e9bd516f6282483b92cfe6074623.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daa5e9bd516f6282483b92cfe6074623.png)
②与③矛盾,故p为偶数.
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解题方法
3 . 阅读下面题目及其证明过程,并回答问题.
如图,在三棱锥
中,
底面
,
,
,
分别是棱
,
的中点.
![](https://img.xkw.com/dksih/QBM/2020/11/10/2590155875131392/2590586443956224/STEM/59e96d8fb6364a7a9a0c2415e5ced222.png?resizew=229)
(1)求证:
平面
;
(2)求证:
.
解答:(1)证明:在
中,
因为
,
分别是
,
的中点,
所以
.
因为
平面
,
平面
,
所以
平面
.
(2)证明:在三棱锥
中,
因为
底面
,
平面
,
所以______.
因为
,且
,
所以______.
因为
平面
,
所以______.
由(1)知
,
所以
.
问题1:在(1)的证明过程中,证明的思路是先证______,再证______.
问题2:在(2)的证明过程中,设置了三个空格.请从下面给出的四个选项中,为每一个空格选择一个正确的选项,以补全证明过程.
①
;②
;③
平面
;④
.
如图,在三棱锥
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63397cda22cb1fad59cf966dfb588643.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ccd4fd4b7a4d6b8ca0c5827c055a9ce7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/080db3af81b29ed10144a1c2e2a4fb8a.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/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/48f3c9abbd78e9a6840ee5f30381daac.png)
![](https://img.xkw.com/dksih/QBM/2020/11/10/2590155875131392/2590586443956224/STEM/59e96d8fb6364a7a9a0c2415e5ced222.png?resizew=229)
(1)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/57f9d682e5d3cc8573574d8d11636758.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e582d73b96ba649378379c3074d506d.png)
(2)求证:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/58cc90fee532e50d319081d571410421.png)
解答:(1)证明:在
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1c025ee3317be1099b7bf03a11e37ed4.png)
因为
![](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/0dc5c9827dfd0be5a9c85962d6ccbfb1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/48f3c9abbd78e9a6840ee5f30381daac.png)
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9f6c1984e2068203465b10ea4ead7916.png)
因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/871502ee0c5d1414cfe81e8409b62d76.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e582d73b96ba649378379c3074d506d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4c9fe3c7e943c3beb7f4bbf345822064.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e582d73b96ba649378379c3074d506d.png)
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/57f9d682e5d3cc8573574d8d11636758.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e582d73b96ba649378379c3074d506d.png)
(2)证明:在三棱锥
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63397cda22cb1fad59cf966dfb588643.png)
因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ccd4fd4b7a4d6b8ca0c5827c055a9ce7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c8690d88536618e3f993dae41a3de66a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
所以______.
因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/080db3af81b29ed10144a1c2e2a4fb8a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/34baf7aadc048e75e776b80eea5b62b5.png)
所以______.
因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4c9fe3c7e943c3beb7f4bbf345822064.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e582d73b96ba649378379c3074d506d.png)
所以______.
由(1)知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9f6c1984e2068203465b10ea4ead7916.png)
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/58cc90fee532e50d319081d571410421.png)
问题1:在(1)的证明过程中,证明的思路是先证______,再证______.
问题2:在(2)的证明过程中,设置了三个空格.请从下面给出的四个选项中,为每一个空格选择一个正确的选项,以补全证明过程.
①
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8a15a004f7d47ed595f063e60075223a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f0d9ef979b9f27a28cbda6923e888ccc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2ffc6952e988d04f22f0fb2f7f0ab7b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1e582d73b96ba649378379c3074d506d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/da48240e7fc3248f773ac1500c15ec14.png)
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4 . 分析法又称执果索因法.若用分析法证明“设
,且
,求证:
”索的因应是______ .
①
;②
;③
;④
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ce613eaa5df46a50174085ef5d1087fb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9e56f4504e0f80fd031c8b5f41832e03.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bff6d61a8eaff20b364a9e3235577c69.png)
①
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/481ee0d1e39e92a4732eea90225eb94c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d6e90787c63ca5b5f1a45e0f6e85aaa1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d8062c16e427bcf70b7ab5c94e8f25a1.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e40e5c797b097deb1f9e89bcb3a405f1.png)
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名校
5 . 用反证法证明“设
,求证
”时,第一步的假设是______________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/127a0d8c1c7d15ed40ec4b8bca0ebdf6.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/485a2d99320384a0857b00ce9ab9e990.png)
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2020-03-20更新
|
474次组卷
|
7卷引用:江苏省连云港市锦屏高级中学2017-2018学年高二下学期期中数学(理)试题
名校
6 . 已知
,求证
的两根的绝对值都小于1,用反证法证明可假设__________
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7b8cfed3e48c308e325045cb87d7bdbb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1146110d4382c714c10de00dd1273b7f.png)
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2016高二·全国·课后作业
7 . △ABC中,若AB=AC,P是△ABC内的一点,∠APB>∠APC,求证:∠BAP<∠CAP,用反证法证明时的假设为________ .
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2017-11-27更新
|
410次组卷
|
6卷引用:同步君人教A版选修1-2第二章2.2.2反证法
(已下线)同步君人教A版选修1-2第二章2.2.2反证法(已下线)同步君人教A版选修2-2第二章2.2.2反证法高中数学人教版 选修1-2(文科) 第二章 推理与证明 2.2.2 反证法高中数学人教版 选修2-2(理科) 第二章推理与证明 2.2.2反证法山西省大同市浑源县第七中学2020-2021学年高二下学期期中数学(文)试题(已下线)2.2.2 间接证明-2020-2021学年高二数学(理)课时同步练(人教A版选修2-2)
8 . 在用反证法证明“已知
,求证:
”时的反设为__________ ,得出的矛盾为________ .
![](https://img.xkw.com/dksih/QBM/2017/5/1/1677586164473856/1678579004612608/STEM/31618af1084147ddaa6deb82df8ecd89.png?resizew=75)
![](https://img.xkw.com/dksih/QBM/2017/5/1/1677586164473856/1678579004612608/STEM/c35f0a87746d490d8077de28f3f2544f.png?resizew=61)
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2017-05-02更新
|
328次组卷
|
2卷引用:山东省菏泽市2016-2017学年高二下学期期中考试数学(文)试题
11-12高二下·福建福州·期中
9 . 如图所示,
平面
,
,过点
作
的垂线,垂足为点
,过点
作
的垂线,垂足为
,求证:
.以下是证明过程:
要证
,
只需证
平面
,
只需证
(因为
),
只需证
平面
,
只需证 ① (因为
),
只需证
平面
,
只需证 ② (因为
),
由
平面
可知上式成立,
所以
.
把证明过程补充完整①___________ ;②__________ .
能力提升
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/10c83f8945042b9c8fb2fbdac9308d62.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/080db3af81b29ed10144a1c2e2a4fb8a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5963abe8f421bd99a2aaa94831a951e9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3d4db9b82b67efe45a02fca32bfcf5dc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2c2bc5e50b8dfa02601c70822252854a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a0ed1ec316bc54c37c4286c208f55667.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/046ced38ceae712960aca9cbf395017a.png)
要证
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/046ced38ceae712960aca9cbf395017a.png)
只需证
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c6deecf9ccb7b7879455050633219e09.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/b03428a8f91a5674cb8f54766c165f7e.png)
只需证
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e40f5583fbfcac922c8ec238c0438452.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d8b73523ef27a2e5f805ae49bd304ba4.png)
只需证
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/9f4c3f9dd5d0343597a7f58a1989b537.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/21665d21bbfb04410c78345de1fd15ae.png)
只需证 ① (因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c152ac8535e5e141342fc11529599841.png)
只需证
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e2ffc6952e988d04f22f0fb2f7f0ab7b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bc9c9cfa597b444b5c9dbae7a825a695.png)
只需证 ② (因为
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/080db3af81b29ed10144a1c2e2a4fb8a.png)
由
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/10c83f8945042b9c8fb2fbdac9308d62.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7bef5239ddbb0972700ce01daf9ee7cf.png)
所以
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/046ced38ceae712960aca9cbf395017a.png)
把证明过程补充完整①
能力提升
![](https://img.xkw.com/dksih/QBM/2018/11/27/2084571035803648/2084651543535616/STEM/79fc1473efcd4ba19a1ea2fe30e3c4c7.png?resizew=149)
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