# Homework Help: Supremums and infimums

1. Jan 6, 2009

1. The problem statement, all variables and given/known data

Show that for all x,y in R (real numbers), sup{x,y}=1/2(x+Y+|X-Y|), and inf{x,y}=1/2(X+Y-|x-y|)

2. Relevant equations

3. The attempt at a solution

i know that the supremum is the lowest upper bound and that the infimum is the largest lower bound. However i really don't know how to apply that to solving this question.

2. Jan 6, 2009

If you have two numbers, one has to be at least as big (greater-than-or-equal-to) the other. Assume that $$x \le y$$. Then
$$\sup\{x,y\} = y$$
$$\inf\{x,y\} = x$$