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(x+2)8的展开式中x6的系数是( ) A.28 B.56 C.112 D.2...
(x+2)8的展开式中x6的系数是( )
A.28
B.56
C.112
D.224
考点分析:
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不等式|x
2-2|<2的解集是( )
A.(-1,1)
B.(-2,2)
C.(-1,0)∪(0,1)
D.(-2,0)∪(0,2)
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已知向量
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=(λ+1,1),
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=(λ+2,2),若(
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+
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)⊥(
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-
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),则λ=( )
A.-4
B.-3
C.-2
D.-1
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已知α是第二象限角,
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=( )
A.
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B.
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C.
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D.
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设集合U={1,2,3,4,5,},集合A={1,2},则∁
UA=( )
A.{1,2}
B.{3,4,5}
C.{1,2,3,4,5}
D.∅
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已知{a
n}是由非负整数组成的无穷数列,该数列前n项的最大值记为A
n,第n项之后各项a
n+1,a
n+2…的最小值记为B
n,d
n=A
n-B
n.
(Ⅰ)若{a
n}为2,1,4,3,2,1,4,3…,是一个周期为4的数列(即对任意n∈N
*,a
n+4=a
n),写出d
1,d
2,d
3,d
4的值;
(Ⅱ)设d是非负整数,证明:d
n=-d(n=1,2,3…)的充分必要条件为{a
n}是公差为d的等差数列;
(Ⅲ)证明:若a
1=2,d
n=1(n=1,2,3,…),则{a
n}的项只能是1或者2,且有无穷多项为1.
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