# Math Help - Elementary set theory problem

1. ## Elementary set theory problem

I apologize, I don't know how to type these symbols in math code.

Give an example of two sets A and B for which (A U B) \ B /= A
The way I think of this is "The elements are either in A or in B, and they are not in B." So I would think that all the elements must be in A, but apparently this is not the case if it is asking me to find two sets where this is not true.

2. This is a trival question. Are you sure you have stated it correctly.
$\begin{array}{l}
A = \left\{ {1,2,3} \right\}\,\& \,B = \{ 2\} \\
A\backslash B = \left\{ {1,3} \right\} \ne A \\
\end{array}
$

3. Wow, now I feel stupid for asking . I guess I wasn't expecting such an easy question to be asked. But thanks for helping.