名校
1 . 用反证法证明命题:“已知
,则
且
”时,应假设______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0dccf7fdc9ff5e9e6ed897ec3a716a35.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/88a6bea084567e3055f0e58499398a46.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5b897700904b00cb79a5a75b82eb3eaf.png)
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解题方法
2 . 已知幂的基本不等式:当
,
时,
.请利用此基本不等式解决下列相关问题:
(1)当
,
时,求
的取值范围;
(2)当
,
时,求证:
;
(3)利用(2)证明对数函数的单调性:当
时,对数函数
在
上是严格增函数.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d33da711e50e96568facb18cef27165.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1419108104429f6df5d5352a05211e36.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/db5e0630a1632f6368fb824ebfdead0d.png)
(1)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7326ea56be82bd616fec7e6aa3c884c8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1419108104429f6df5d5352a05211e36.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ca16bee4a8ecee60c31f9aaac02539b0.png)
(2)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d33da711e50e96568facb18cef27165.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/27eb687fdf1568ab06ce8119845823c9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c92098b3da769963a2320cf1d8dad00a.png)
(3)利用(2)证明对数函数的单调性:当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1d33da711e50e96568facb18cef27165.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/82869dad28f771d088772a2c2b08b187.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d562dc22dfb3b81d0c3f88b54d063c2f.png)
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3 . 用反证法证明命题“设
,如果
能被5整除,那么
中至少有一个能被5整除”,假设应该是( )
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4e248e4276d630c02ff008f332f4b3fc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/18f0281e6bbdbe08beeccb55adf84536.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/632244ea6931507f8656e1cc3437d392.png)
A.![]() | B.![]() |
C.![]() ![]() | D.![]() |
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4 . 若要用反证法证明“三角形的内角中最多有一个钝角”,需要假设“三角形的内角中_________ .
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5 . 设
、
. “若
,则
或
”是一个真命题.用反证法证明这个命题是真命题时,可以先假设该命题的结论不成立,即:_____________ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/95cccdff49c3efe6e7a7dbbf69db9319.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6f9e131cdd242d56b6dba05ab3363ef3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0fde64f4d3c38e43fbdee24eadc4b0dd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eec336faee8689281a6f6b465e7fcff9.png)
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解题方法
6 . 设整数集合
,其中
,且对于任意
,若
,则
.
(1)请写出一个满足条件的集合A;
(2)证明:任意
,
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/eab8bf709a13b3d6cea5bf2b05c92019.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8d1c5d7e92a7d6c61e007cd9313b1b6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4b836bde5106e78caeb728ff3353bee7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/269c7a915fc171ac7ad84c09883a6dd5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1250b7f54f3a23a5e52b2e4aa0fc0050.png)
(1)请写出一个满足条件的集合A;
(2)证明:任意
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/361b9733dc8c4896ce0501d1a3ddf3a9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7848c89302a41e9576530313fc3e61b8.png)
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解题方法
7 . 已知代数式
和
.
(1)若
,求不等式
的解集;
(2)若
,证明
中至少有一个数不小于
;
(3)若
,不等式
对任意实数
恒成立,试确定实数
满足的条件.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2fe56a82278b144101fda1fa2cf59703.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8c0a82f3b0b621e05cf6e77cddb0628e.png)
(1)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3278317e48e20b5aae4912d0cfdce545.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb6ae0a7e5eeda987af2130d0ba69bf1.png)
(2)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/da67075d5f20954afe0232112e159ac9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d33f8ea9598f0d9134721b35565d28e2.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/533a7b702ada1dd80123e4041271d521.png)
(3)若
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/94440d3e4c073f94f2b266ff99d50e74.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a5d5b84e3d3af2112a4f066c2a9f1387.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/81dea63b8ce3e51adf66cf7b9982a248.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/632244ea6931507f8656e1cc3437d392.png)
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8 . (1)设
,
,求证:
;
(2)已知
,
,且
.证明:
或
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/94440d3e4c073f94f2b266ff99d50e74.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/67ca5fd57c2c2fcc3c7a574fdd1467d9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/54d8bf9316bb1dfb0559333ce56b35a6.png)
(2)已知
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/08115d6d9f876dea921a4d32260ff1fb.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/061813f1ec633c5c4c393c4de7938322.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/6f9e131cdd242d56b6dba05ab3363ef3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ef8e5b510c343f9d3d626fa1a4b36bad.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e36ffaf917dcebc8719f2ca539a774ec.png)
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9 . 设
,而
为S的一个8元子集.求证:
(1)存在非零自然数k,使得方程
至少有3组不同的解;
(2)对于S的7元子集
,(1)中的结论不再总是成立.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/06018a972e02a43b95f5c78aca784610.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d7bf032b085c415f6ce188bd9be0afe6.png)
(1)存在非零自然数k,使得方程
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aae335e59364467c2ad9d5602f220af2.png)
(2)对于S的7元子集
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f7c1f4838725717094b55f5d82a3e2ca.png)
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名校
10 . 命题“
,若
,则
或
”用反证法证明时应假设为____ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/73254f32b6da29ecc32df2e9f87a4c97.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f71a7888032847705f122e3ed0743ea.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0b550ee821ee1838384835e81fc34b67.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5a3c442579603164f3fc19458677d307.png)
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