If X and Yare two sets such that X∩Y=X∪Y, then
X⊂Y,X≠Y
Y⊂X, Y≠X
X=Y
none of these
X⊂Y⇒ X∩Y=X, X∪Y=YY⊂X ⇒ X∩Y=Y, X∪Y=X.So, X∩Y=X∪Y ⇒X=Y