Question

Give examples to show that
If $A\subset B$, then $A\cup B=B$ and $A\cap B=A$.

Answer 1

Let $A=\{a,b,c\}$
$B=\{a,b,c,d\}$

$A\subset B$

$A\cup B=\{a,b,c,d\}=B$

$A\cap B=\{a,b,c\}=A$