Answer with Step-by-step explanation:
We are given that two sets A and B

We have to prove show that 
Suppose , x belongs to [tex}A\cap B[/tex]
Then , 
Then, 
If, 
Then, 
If
Then, it is not necessary that x belongs to A .
If x belongs to A then

If x does not belongs to A then

But, if x belongs to A then x is also belongs to B because A is a subset of B.
Then, 