Recent content by yangbin990

Really appreciate everyone's help, especially Stephen's explanation. And I will spend some time to digest micromass's reply as well.

Hi, I am teaching myself the discrete math using the "Discrete Mathematics Lecture Notes, Yale University, Spring 1999". And I don't how to prove the practice question below: Prove that |A∪B|+|A∩B| = |A|+|B|. The textbook provide answer like below: The common elements of A and B are...