设集合A={x2,2x-1,-4},B={x-5,1-x,9},若A∩B={9},求x的值及A∪B.
问题描述:
设集合A={x2,2x-1,-4},B={x-5,1-x,9},若A∩B={9},求x的值及A∪B.
答
∵集合A={x2,2x-1,-4},B={x-5,1-x,9},且A∩B={9},
∴x2=9或2x-1=9,
解得:x=3或-3或5,
当x=3时,A={-4,9,5},B={9,-2},不合题意;
当x=-3时,A={-4,9,-7},B={9,4,-8},符合题意;
当x=5时,A={-4,9,25},B={9,0,-4},不合题意,
∴x的值为-3,
即A={-4,9,-7},B={9,4,-8},
则A∪B={-4,-8,-7,4,9}.