Question

Any set $A$ such that $A\cup A=\{11,13,5,6\},$ then $A=$

• A. $\{11,13,5,6\}$
• B. $\{5,6\}$
• C. $\left\{\right\}$

Answer 1

The correct option is A $\{11,13,5,6\}$

Given a set $A$ such that $A\cup A=\{11,13,5,6\}$
Now, by idempotent law, i.e., $A\cup A=A$
$\Rightarrow A=\{11,13,5,6\}$