The expression $A \cup C'$ refers to the union of set $A$ and the complement of set $C$. Here's a breakdown of the components:

1. $A$: This is the first set.
2. $C'$: This is the complement of set $C$, which means all the elements that are not in $C$ but are within the universal set.
3. $\cup$: This symbol represents the union, which includes all elements that are either in $A$ or in $C'$ (or in both).

Thus, $A \cup C'$ contains all elements that are in set $A$, combined with all elements not in set $C$.

If you have specific sets for $A$ and $C$, I can calculate the union for you.

Would you like more details or clarification?

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Relative Questions:

1. What is the difference between union and intersection in set theory?
2. How do you find the complement of a set in practice?
3. Can the union of two sets be equal to one of the sets?
4. How does the complement of a set relate to the universal set?
5. How would the expression change if we had $A \cap C'$ instead?

Tip: In set theory, the union of two sets combines all unique elements, ensuring no duplicates between the sets.