Let $U=\{1, 2, 3, 4, 5, 6, 7, 8, 9\}$,$A=\{1, 2, 3, 4\}$,$B=\{2, 4, 6, 8\}$,and $C=\{3, 4, 5, 6\}$. Find $(A \cup B)'$.

Let $A$ and $B$ be two non-empty subsets of a set $X$ such that $A$ is not a subset of $B$,then

Let $U$ be the universal set and $A \cup B \cup C = U$. Then $\{ (A - B) \cup (B - C) \cup (C - A)\} '$ is equal to

Fill in the blank to make the following a true statement:
$U^{\prime} \cap A = \ldots$

Let $U$ be the set of all triangles in a plane. If $A$ is the set of all triangles with at least one angle different from $60^{\circ},$ what is $A^{\prime}$?

For each positive real number $\lambda$,let $A_\lambda$ be the set of all natural numbers $n$ such that $|\sin(\sqrt{n+1}) - \sin(\sqrt{n})| < \lambda$. Let $A_\lambda^c$ be the complement of $A_\lambda$ in the set of all natural numbers. Then,