(完整版)洪帆《离散数学基础》(第三版)课后习题答案

第1章 集合

1、列举下列集合的元素 (1) 小于20的素数的集合 (2) 小于5的非负整数的集合 (3) {i|i?I,i2?10i?24?0且5?i?15} 答:(1) {1,3,5,7,11,13,17,19}

(2) {0,1,2,3,4} (3) {5,6,7,8,9,10,11}

2、用描述法表示下列集合 (1) {a1,a2,a3,a4,a5} 答:{ai|i?I,1?i?5} (2) {2,4,8,L} 答:{2i|i?N} (3) {0,2,4,L100}

答:{2i|i?Z,0?i?50}

3、下面哪些式子是错误的? (1) {a}?{{a}} 答:正确 (2) {a}?{{a}} 答:错误 (3) {a}?{{a},a} 答:正确 (4) {a}?{{a},a} 答:正确

4、已给S?{2,a,{3},4}和R?{{a},3,4,1},指出下面哪些论断是正确的?哪些是错误的? (1) {a}?S 错误

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(2) {a}?R 正确 (3) {a,4,{3}}?S 正确 (4) {{a},1,3,4}?R 正确 (5)R?S 错误 (6) {a}?S 正确 (7) {a}?R错误 (8) ??R正确 (9) ??{{a}}?R 正确 (10) {?}?S错误 (11) ??R错误 (12) ??{{3},4}正确

5、 列举出集合A,B,C的例子,使其满足A?B,B?C且A?C

答:A?{a},B?{{a}},显然A?B,C?{{{a}}},显然B?C,但是A?C。

6、 给出下列集合的幂集 (1) {a,{b}}

答:幂集{?,{a},{{b}},{a,{b}} (2) {?,a,{a}}

答:幂集{?,{?},{a},{{a}},{?,a},{?,{a}},{a,{a}},{?,a,{a}}} 7、设A?{a},给出A和2A的幂集

答:2A?{?,{a}} 22?{?,{{?}},{{a}},{?,{a}}}

8、 设A?{a1,a2,L,a8}由B17和B31所表示的A的子集各是什么?应如何表示子集{a2,a6,a7}和{a1,a3} 答:B17?B00010001?{a4,a8}

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AB31?B00011111?{a4,a5,a6,a7,a8}

{a2,a6,a7}?B01000110?B70,{a1,a3}?B10100000?B160

9、 设U?{1,2,3,4,5},A?{1,4},B?{1,2,5},C?{2,4},确定集合: (1) A?B? (2) (A?B)?C? (3) A?(B?C) (4)(A?B)?(A?C) (5) (A?B)? (6) A??B? (7) (B?C)? (8)B??C? (9) 2A?2C (10)2A?2C 答:(1) B??{3,4},A?B??{4}

(2) A?B?{1},C??{1,3,5},(A?B)?C??{1,3,5} (3) B?C?{2},A?(B?C)?{1,2,4}

(4) A?B?{1,2,4,5},A?C?{1,2,4},(A?B)?(A?C)?{1,2,4} (5) (A?B)??{2,3,4,5} (6) A??{2,3,5},A??B??{2,3,4,5} (7) B?C?{1,2,4,5},(B?C)??{3} (8) B??{3,4},C??{1,3,5},B??C??{3}

,,4}},2A?2C?{{1},{1,4}} (9) 2A?{?,{1},{4},{1,4}},2C?{?,{2},{4}{2(10) 2A?2C?{?,{4}}

10、 给定自然数集N的下列子集:

A?{1,2,7,8},B?{i|i2?50},C?{i|i可被3整数,0?i?30}

D?{i|i?2k,k?Z,0?k?6}

求下列集合: (1) A?(B?(C?D)) 答:B?{1,2,3,4,5,6,7},

C?{0,3,6,9,12,15,18,21,24,27,30},D?{1,2,4,8,16,32,64}

A?(B?(C?D))?{0,1,2,3,4,5,6,7,8,9,12,15,16,18,21,24,27,30,32,64} (2) A?(B?(C?D))??

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(3) B?(A?C)

解:A?C?{0,1,2,3,6,7,8,9,12,15,18,21,24,27,30},B?(A?C)?{4,5} (4) (A??B)?D

解:A??B?B?A?{3,4,5,6},(A??B)?D?{1,2,3,4,5,6,8,16,32,64}

11、 给定自然数集N的下列子集

A?{n|n?12},B?{n|n?8},C?{n|n?2k,k?N},D?{n|n?3k,k?N} E?{n|n?2k?1,k?N}

将下列集合表示为由A,B,C,D,E产生的集合:

(1) {2,4,6,8} (2){3,6,9} (3){10} (4){n|n?3或n?6或n?9} (5) {n|n是偶数且n?10或n是奇数且n?9} (6) {n|n是6的倍数}

答:A?{1,2,3,4,5,6,7,8,9,10,11},B?{1,2,3,4,5,6,7,8}

C?{2,4,6,8,L},D?{3,6,9,12,L},E?{1,3,5,7,L} {2,4,6,8}?B?C {3,6,9}=A?D {10}=((A?B)?D)?E

(4){n|n?3或n?6或n?9}?{3}?{6}?{9,10,11,12,L}

?{3,6,9,10,11,12,L}?(A?D)?B?

(5) {2,4,6,8,10,11,13,15,L}?((A?E)?(E?B))?((A?D)?B) (6) {n|n是6的倍数}?{6,12,18,24,30L}?C?D

12、 判断以下哪些论断是正确的,哪些论断是错误的,并说明理由。 (1) 若a?A,则a?A?B

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