Review:(1)subsetThesetAisasubsetofthesetBifeveryelementofAisanelementofB.whenthisisso,AisincludedinB,writtenAB,andBincludesA,writtenBA.(2)Properties:(i)ForallsetsA,ΦAandAA.(ii)ForallsetsAandB,A=BifandonlyifABandBA.(iii)ForallsetsA,BandC,ifABandBC,thenAC.(3)Propersubset:LetAbeasubsetofB.thenAisapropersubsetofBifAisnotequaltoBitself.ThusthereissomeelementofBnotinA.ThesubsetAisthensaidtobeproper(orstrictly)includedinB,andthisiswrittenAB.ΦA(A≠Φ)(4)AB,FirstcaseA=Φ.SecondcaseA≠Φ.(5)A={a1,a2,a3,……，an}Thenumberofsubsets:2nThenumberofpropersubsets:2n-1Thenumberofnon-emptysubsets:2n-1Thenumberofnon-emptypropersubsets:2n-21.1.3集合的基本运算观察集合A,B,C元素间的关系:(1)A={4，5，6，8}，B={3，5，7，8}，C={3，4，5，6，7，8}(2)A={x|x是有理数}，B={x|x是无理数}，C={x|x是实数}定义一般地,由属于集合A或属于集合B的所有元素组成的集合叫做A与B的并集（unionset）记作AB∪即AB={x|xA,∪∈或xB}∈读作A并BABAB∪例1.设A=｛x|-1
