集合习题(难)附答案
1.(2013·广东) 设集合M ={x |x 2+2x =0,x ∈R },N ={x |x 2-2x =0,x ∈R },则M ∪N =( )
A .{0}
C .{-2,0}
[答案] D
[解析] 化简两个集合,得M ={-2,0},N ={0,2},则M ∪N ={-2,0,2},故选D.
2.(2013·天津) 已知集合A ={x ∈R ||x |≤2},B ={x ∈R |x ≤1},则A ∩B =( )
A .(-∞,2]
C .[-2,2]
[答案] D
[解析] 易知A ={x ∈R |-2≤x ≤2},故A ∩B ={x |-2≤x ≤1}.故选D.
3.(2013·北京朝阳) 设集合A ={x |x 2+2x -3>0},集合B ={x |x 2-2ax -1≤0,a >0}.若A ∩B 中恰含有一个整数,则实数a 的取值范围是( )
3⎛0, A. 4⎝⎭
⎡3⎫C. ⎢4⎪ ⎣⎭
[答案] B
[解析] A ={x |x 2+2x -3>0}={x |x >1或x 0,f (0)=-1
⎧4-4a -1≤0,整数,则这个整数为2,所以有f (2)≤0且f (3)>0,即⎨所以9-6a -1>0,⎩
3⎧⎪a ≥4,⎡34⎫B. ⎢4,3⎪ ⎣⎭D .(1,+∞) B .[1,2] D .[-2,1] B .{0,2} D .{-2,0,2}
⎨4⎪⎩a
4.(2014·原创) 设有限集合A ={a 1,a 2,„,a n },则∑a i 叫做集合A 的和,
i =1n
记作S A . 若集合P ={x |x =2n -1,n ∈N *,n ≤4},集合P 的含有3个元素的全体子集分别为P 1,P 2,„,P k ,则∑SP i =________.
i =14
[答案] 48
[解析] 易知P ={1,3,5,7},则含有3个元素的子集共有4个,分别是P 1={1,3,5},则SP 1=9,P 2={1,3,7},则SP 2=11,P 3={1,5,7},则SP 3=13,P 4={3,5,7},即SP 4=15,所以∑SP i =SP 1+SP 2+SP 3+SP 4=
48.
i =14
1.非空数集A ={a 1,a 2,a 3,„,a n }(n ∈N *) 中,所有元素的算术平均数记为E (A ) ,即E (A ) =a 1+a 2+a 3+„+a n . 若非空数集B 满足下列两个条件:①B ⊆n
A ;②E (B ) =E (A ) ,则称B 为A 的一个“保均值子集”.据此,集合{1,2,3,4,5}的“保均值子集”有( )
A .5个
C .7个
[答案] C
[解析] 非空数集A ={1,2,3,4,5}中,所有元素的算术平均数E (A ) =1+2+3+4+5=3,所以集合A 的“保均值子集”有:{3},{1,5},{2,4},{3,1,5},5
{3,2,4},{1,5,2,4},{1,2,3,4,5},共7个.
B .6个 D .8个
已知茎叶图列举了集合U 中的所有元素,设A ={3,6,9},B ={3,5,12},则(∁U A ) ∩B =________.
[答案] {5,12}
[解析] 由茎叶图可知:U ={3,5,6,9,12,13},则∁U A ={5,12,13}故(∁U A ) ∩B
={5,12}.
———————————————
已知全集U =R ,集合A ={x |y =ln(3x -1)},B ={y |y =sin(x +2)},则(∁U A ) ∩B =( )
1⎤⎛B. 0,3⎥ ⎝⎦
D .∅ ⎛1⎫A. 3⎪ ⎝⎭1⎡C. ⎢-1,3 ⎣⎦
[答案] C
⎛1⎫[解析] ∵A ={x |y =ln(3x -1)}= 3,+∞⎪,B ={y |y =sin(x +2)}=[-1,1],⎝⎭
1⎛∴∁U A = -∞,3, ⎝⎦
1⎡∴(∁U A ) ∩B =⎢-1,3,故选C. ⎣⎦