Draw a Venn Diagram showing Circles A and B intersecting.
(A U B)` is then the area that lies outwith the circles and their intersection.
Actually it's A' (intesected with) B'.
This is demorgan's theorem, you should check it out! It's pretty useful for these things :)
For a venn diagram, it's all the space outside both circles.
Its a DeMorgan law. Actually it should be (AUB)'=A' intersect B' .In venn diagram it means (AUB)' means the things that are not in A or B. A' intersect B' means the things that are not in A and the things thar are not in B.