来自段爱琴的问题
设全集为R,A={x2,2x-1,-4},B={x-5,1-x,9}(1)若x=-3,求∁R(A∩B);(2)若{9}⊆A∩B,求A∪B.
设全集为R,A={x2,2x-1,-4},B={x-5,1-x,9}
(1)若x=-3,求∁R(A∩B);
(2)若{9}⊆A∩B,求A∪B.
1回答
2020-02-08 10:02
设全集为R,A={x2,2x-1,-4},B={x-5,1-x,9}(1)若x=-3,求∁R(A∩B);(2)若{9}⊆A∩B,求A∪B.
设全集为R,A={x2,2x-1,-4},B={x-5,1-x,9}
(1)若x=-3,求∁R(A∩B);
(2)若{9}⊆A∩B,求A∪B.
(1)∵x=-3,
∴A={9,-7,-4},B={-8,4,9},
∴A∩B={9},
∴∁R(A∩B)=(-∞,9)∪(9,+∞);
(2)若{9}⊆A∩B,知9∈A,
①若x2=9,则x=±3,
当x=3时,A={9,5,-4},x-5=1-x,与B集合的互异性矛盾;
当x=-3时,A={9,-7,-4},B={-8,4,9},满足题意.
故A∪B={-8,-7,-4,4,9}.
②若2x-1=9,则x=5,
此时A={25,9,-4},B={0,-4,9},A∩B={-4,9},满足题意.
故A∪B={-4,0,9,25},
综上所述,A∪B={-8,-7,-4,4,9}或A∪B={-4,0,9,25}.