Recent content by congtongsat

much appreciated. cleared things up for me.

Problem: (i)A\subseteqB \Leftrightarrow A\cupB = B (ii) A\subseteqB \Leftrightarrow A\capB = A and For subsets of a universal set U prove that B\subseteqA^{c} \Leftrightarrow A\capB = empty set. By taking complements deduce that A^{c}\subseteqB \Leftrightarrow A\cupB = U. Deduce that...

Problem: We define half infinite intervals as follows: (a, \infty) = {x\in R | x>a}; [a, \infty) = {x\in R | x\geqa}; Prove that: (i) (a, \infty) \subseteq [b, \infty) \Leftrightarrow a\geqb, (ii) [a, \infty) \subseteq (b, \infty) \Leftrightarrow a>b. I've got pretty much no idea how...