Complete the following questions concerning the above claim and "proof": (1) Determine whether the “proof" is rigorous. Identify the issues in the "proof", if any. (2) Determine whether the claim is true or false. Justify the answer in part (3). (3) If the the claim is true and the “proof" is not rigorous, then provide a correct and rigorous proof. If the claim is false, give a concrete counterexample. Hint. Complete the parts as instructed. If the claim is false, then (obviously) there is no way the “proof" could be correct.

Elementary Geometry For College Students, 7e
7th Edition
ISBN:9781337614085
Author:Alexander, Daniel C.; Koeberlein, Geralyn M.
Publisher:Alexander, Daniel C.; Koeberlein, Geralyn M.
ChapterP: Preliminary Concepts
SectionP.1: Sets And Geometry
Problem 2E
Question
Problem 4.4 (Grade a "Proof"). Study the following claim as well as the "proof":
Claim. For all sets A, B and C, if ACBUC then P(A) C P(B)U P(C).
"Proof". Let A, B and C be sets. Assume A CBUC. Let x be an arbitrary
element and suppose r € P(A). Note that r E P(A) implies r E A. Then, since
ACBUC, we get r e BUC, which then implies x e B or x € C. Therefore, we
see r € P(B) or x € P(C), which simply means r E P(B)U P(C). Since every
x in P(A) must be in P(B) U P(C), we conclude P(A) C P(B)U P(C).
Complete the following questions concerning the above claim and "proof":
(1) Determine whether the "proof" is rigorous. Identify the issues in the "proof",
if any.
(2) Determine whether the claim is true or false. Justify the answer in part (3).
(3) If the the claim is true and the "proof" is not rigorous, then provide a correct and
rigorous proof. If the claim is false, give a concrete counterexample.
Hint. Complete the parts as instructed. If the claim is false, then (obviously) there is no
way the "proof" could be correct.
Transcribed Image Text:Problem 4.4 (Grade a "Proof"). Study the following claim as well as the "proof": Claim. For all sets A, B and C, if ACBUC then P(A) C P(B)U P(C). "Proof". Let A, B and C be sets. Assume A CBUC. Let x be an arbitrary element and suppose r € P(A). Note that r E P(A) implies r E A. Then, since ACBUC, we get r e BUC, which then implies x e B or x € C. Therefore, we see r € P(B) or x € P(C), which simply means r E P(B)U P(C). Since every x in P(A) must be in P(B) U P(C), we conclude P(A) C P(B)U P(C). Complete the following questions concerning the above claim and "proof": (1) Determine whether the "proof" is rigorous. Identify the issues in the "proof", if any. (2) Determine whether the claim is true or false. Justify the answer in part (3). (3) If the the claim is true and the "proof" is not rigorous, then provide a correct and rigorous proof. If the claim is false, give a concrete counterexample. Hint. Complete the parts as instructed. If the claim is false, then (obviously) there is no way the "proof" could be correct.
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