Question

If set A X B=B X A then which of the following sets may satisfy?

(a) A={1, 2, 3}, B={1, 2, 3, 4}

(b) A={1, 2}, B={2, 1}

(c) A={1, 2, 3}, B={2, 3, 4}

(d) None of the mentioned

I had been asked this question in quiz.

This is a very interesting question from Cartesian Product of Sets topic in section Basic Structures: Sets, Functions, Sequences, Sums and Matrices of Discrete Mathematics

Answer 1

Right answer is (b) A={1, 2}, B={2, 1}

To explain: For set A X B = B X A, this is possible only when set A = B.