A△B=(A∖B)∪(B∖A)A \triangle B = (A\setminus B) \cup (B\setminus A) A△B=(A∖B)∪(B∖A) =(A∪B)∖(A∩B) = (A \cup B) \setminus (A \cap B)=(A∪B)∖(A∩B)