1 . 已知A,B,C,P为空间内不共线的四点,G为
的重心.
(1)证明:
;
(2)若向量
,
,
的模长均为2,且两两夹角为
,求
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/15c0dbe3c080c4c4636c64803e5c1f76.png)
(1)证明:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/fb74becf9bdf4d13e122ac50180e1f57.png)
(2)若向量
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/454a02d14e3371707f979ea0cd7b9412.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ee2638bcdc57e4e56a9b61430c9edfbf.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f7b683529d8299e73e36ef06d0b1463d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ac1a63ab608517bb10aa036783dfb51f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7d7dcb895ec70ebe01260e881414b4e1.png)
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2 . 已知
,
,
,用反证法证明“
与
至少有一个不小于3”的假设是( )
![](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/5be97cd1c7111b654d87d8fbb63b6a84.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bc8ee230708950226bacead117cdbf6e.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/393442926e96fddbce94ab3aeca809d3.png)
A.![]() ![]() | B.![]() ![]() |
C.![]() ![]() | D.![]() ![]() |
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名校
3 . 下列说法或运算正确的是( )
A.![]() |
B.用反证法证明“一个三角形至少有两个锐角”时需设“一个三角形没有锐角” |
C.“![]() ![]() ![]() ![]() |
D.直线![]() ![]() |
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