proof by contradiction:
assume : P(A int B) != P(A) int P(B)
now,
A={1,2}
B={2,3}
P(A)={ empty set, {1}, {2}, {1,2} }
P(B)={ empty set, {3}, {2}, {3,2} }
A intersection B = {2}
P(A int B)={ empty set, {2} } = P(A) int P(B), which is contradicting our assumption.
therefore our assumption is wrong. hence the statement is proved.