Show that if A is an infinite set, then whenever B is a set, AUB is also an infinite set.

Elements Of Modern Algebra
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ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter7: Real And Complex Numbers
Section7.1: The Field Of Real Numbers
Problem 25E: If and are positive real numbers, prove that there exist a positive integer such that . This...
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Show that if A is an infinite set, then whenever B is a set, AUB is also an infinite set.
Solution: If AUB were finite, then it would have n elements for some natural number n. But A
already has more than n elements, because it is infinite, and AUB has all the elements that A has,
so AUB has more than n elements. This contradiction shows that AUB must be infinite.
Transcribed Image Text:Show that if A is an infinite set, then whenever B is a set, AUB is also an infinite set. Solution: If AUB were finite, then it would have n elements for some natural number n. But A already has more than n elements, because it is infinite, and AUB has all the elements that A has, so AUB has more than n elements. This contradiction shows that AUB must be infinite.
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