Question

Let A =(2,5,6,8) and B=(5,7,9,1).findAuB

Answer 1

AuB means all terms of set A and set B. And also not writing the same number twice from the sets write it only once.
AuB={1,2,5,6,7,8,9}

Answer 2

since they have no comman number except5 so their union is(1256789)