Answer to Question #269814 in Discrete Mathematics for auni

Question

Let A and B be subsets of a universal set U. Show that A ⊆ B if and only if B ⊆ A.

Answer 1

if A ⊆ B then $A=A\cap B$

if B ⊆ A then $B=A\cap B$

so, $A=B=A\cap B$