Suppose A and B are non-empty sets of real mumbers that are both bounded above. (a) Prove that, if A C B, then sup A < sup B. (b) Prove that sup AUB = max{sup A, sup B}. (c) Prove that, if ANB + Ø, then sup AnB < min{sup A, sup B}. Give an example to show that equality need not hold.

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter2: Equations And Inequalities
Section2.6: Inequalities
Problem 80E
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a)To prove this directly, you'd suppose that A is a subset of B.  Then you'd need to show that sup(A)≤sup(B)sup(A)≤sup(B).  Since A is bounded above, sup(A) is the least upper bound for A which, by definition of l.u.b., is less than or equal to all upper bounds for A.  

b)Note that, max{sup(A), sup(B)} is either sup(A) or sup(B).  So you have a couple of natural cases to break things down into. 

c) I am not sure of

 

Suppose A and B are non-empty sets of real numbers that are both bounded above.
(a) Prove that, if AC B, then sup A< sup B.
(b) Prove that sup AUB = max{sup A, sup B}.
(c) Prove that, if AnB #0, then sup ANB < min{sup A, sup B}. Give an example
to show that equality need not hold.
Transcribed Image Text:Suppose A and B are non-empty sets of real numbers that are both bounded above. (a) Prove that, if AC B, then sup A< sup B. (b) Prove that sup AUB = max{sup A, sup B}. (c) Prove that, if AnB #0, then sup ANB < min{sup A, sup B}. Give an example to show that equality need not hold.
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