Question

设集合A={1,a-1},集合B={-2,a,b}若A交B={2},则A并B=?

Answer 1

A交B={2},则A中a-1=2,所以a=3

B中就只能是b=2了

A={1,2},B={-2,3,2}

所以A并B={-2,1,3,2}