1.4集合的运算习题1.41.全集},,,,,,,{hgfedcbaU,令集合A,B,C,D分别为},,,{gcbaA,},,,{gfedB,},,{fcaC,},{hfD.试分别计算(1)BA;(2)CB;(3)DA;(4)CBA)(;(5)D;(6)CB;(7))(CBA;(8)CDA)(;(9)CA;(10)CBA.解(1)},,,,,,{gfedcbaBA.(2)}{fCB.(3)},,,{gcbaDA.(4)}{},,{}{}{)(gfcagCgCBA.(5)},,,,,{gedcbaD.(6)},,,,{}{},,,,,{)()(gedcafgfedcaCBCBCB.(7)},,{},,,,,{},,,{)(gcagfedcagcbaCBA.(8)},,{},,,,{},,,,,{)(fcahgedbhfgcbaCDA.(9)},,{},,,,{hedgfcbaCA.(10)},,,,,,{gfedcbaCBA.2.设CA且CB,则CBA,进而CBA.证对于任意BAx,则Ax或Bx.因为CA且CB,所以有Cx,因此CBA.由于ABA且BAA,而CBA,所以CBA.3.证明DeMorgan律.证先证明BABA.对于任意BAx,则BAx,由此得出Ax且Bx,因此Ax且Bx,即BAx,所以BABA.另一方面,若BAx,则Ax且Bx,于是Ax且Bx,进而BAx,因此BAx,所以BABA.故BABA.类似可证BABA.4.对于集合BA,,证明:BA当且仅当AB.证()假定BA.若对于Bx,则Bx,因为BA,于是Ax,这时Ax,所以AB.()假定AB.对于任意Ax,则Ax.因为AB,所以Bx,即Bx,进而BA.5.设BAf:,对于任意AX及AY,证明:)()()(YfXfYXf.一般来说)()()(YfXfYXf,举例说明之.证因为XYX,所以)()(XfYXf.同样因为YYX,所以)()(YfYXf.于是有)()()(YfXfYXf.例如取},,{cbaA,}2,1{B,令BAf:,2)()(bfaf,1)(cf.再取},{caX,},{cbY,这时}2,1{)(Xf,}2,1{)(Yf,因此}2,1{)()(YfXf.由于}1{})({)(cfYXf,所以有)()()(YfXfYXf.6.对于任意集合CBA,,,证明:BCACBA)()(.证)()()()(CBACBACBACBA=.)()(BCABCA7.设CBA,,是集合,下列命题是否成立,为什么?(1)若CABA,则CB.(2)若CABA,则CB.(3)若CABA且CABA,则CB.解(1)不成立.例如,},,{cbaA,},{baB,},{cbC,这时显然有CABA,但CB.(2)不成立.例如,}{aA,},{baB,},{caC,这时显然有CABA,但CB.(3)成立.因为)()()()(CBABCABBABBCCCACBACBCA)()()()(.8.对于任意集合A和B,证明:(1))()()(BAPBPAP.(2))()()(BAPBPAP,并举例说明)()()(BAPBPAP不成立.证(1)任意)()(BPAPX,则)(APX且)(BPX,于是AX且BX,因此,BAX,进而)(BAPX,所以)()()(BAPBPAP.又因为ABA,于是)()(APBAP.同样,)()(BPBAP,所以)()()(BPAPBAP.故)()()(BAPBPAP.(2)因为BAA,于是)()(BAPAP.同样,)()(BAPBP,所以)()()(BAPBPAP.例如},{baA,},{cbB,于是{)(AP,}},{},{},{baba且{)(BP,}},{},{},{cbcb,因此{)()(BPAP,}},{},,{},{},{},{cbbacba,这时6|)()(|BPAP.而},,{cbaBA,所以82|)(|3BAP.显然有)()()(BAPBPAP.9.设BA,是集合,证明:BA当且仅当BA.证()若BA,根据差运算的定义知BA.()若BA,对于任意Ax,则Bx,否则BA,因此BA.10.对于任意集合CBA,,,分别找出使下列等式成立的最简单的充要条件:(1)ACABA)()(.(2))()(CABA.(3))()(CABA.解(1))()()()()(CBACABACABA)(CBACBA,而ACBA)(的充要条件是A与CB没有公共元素,即CBA.于是,ACABA)()(的充要条件是CBA.(2))()()()()(CBACABACABA)(CBACBA,而)(CBA的充要条件是ACB.于是,)()(CABA的充要条件是ACB.(3))()(CABA的充要条件是CABA,这就是最简单的)()(CABA的一个充要条件.11.设BA,是集合,...