Answer
{1,2,3,4,5,6,7,8,9}
Work Step by Step
U means union. A U B means the union of all of the elements in A and B.
A={1,3,4,5,9}
B={2,4,6,7,8}
If we put all of the numbers together we get: 1,3,4,5,9 and 2,4,6,7,8.
We don't list any element more than once, so although 4 is in both sets, we only list it once. Now we have: 1,3,4,5,9, and 2,6,7,8.
Putting them in order for readability we get {1,2,3,4,5,6,7,8,9}.
