Hello to everyone!
Could someone say me the answer of the following set question?
A ∩ B ⊆ A ∪ B = Prove!
It needs a proving like the example below:
A ∩ B = {x|x€A and x€B}
Thanks,
Best wishes.
Lets consider the case where both sets are non-empty. the result holds trivially in the cases where both are empty or $\displaystyle A \cap B$ is empty. (why?)
to prove $\displaystyle A \cap B \subseteq A \cup B$ we must show that if $\displaystyle x \in A \cap B$, then $\displaystyle x \in A \cup B$.
Assume $\displaystyle x \in A \cap B$. Then $\displaystyle x \in A$ and $\displaystyle x \in B$. Clearly it holds that $\displaystyle x
\in A$ or $\displaystyle x \in B$, so that $\displaystyle x \in A \cup B$. Thus, $\displaystyle A \cap B \subseteq A \cup B$