18. Prove the following proposition: For all integers a and b, if 3 divides (a? + b?), then 3 divides a and 3 divides b.

Elements Of Modern Algebra
8th Edition
ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter2: The Integers
Section2.5: Congruence Of Integers
Problem 35E
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Question 18
STOI WIII
a counterexample or a proof.
For each integer n, if n is odd and n is not a multiple of 3, then
n2 = 1 (mod 24).
18. Prove the following proposition:
For all integers a and b, if 3 divides (a? + b2), then 3 divides a and 3
divides b.
19. Is the following proposition true or false? Justify your conclusion with a
counterexample or a proof.
For each integer a, 3 divides a + 23a.
20. Are the following statements true or false? Either prove the statement is true
or provide a counterexample to show it is false.
(a) For all integers a and b, if a · b = 0 (mod 6), then a = 0 (mod 6) or
h- 0 (mod 6)
Transcribed Image Text:STOI WIII a counterexample or a proof. For each integer n, if n is odd and n is not a multiple of 3, then n2 = 1 (mod 24). 18. Prove the following proposition: For all integers a and b, if 3 divides (a? + b2), then 3 divides a and 3 divides b. 19. Is the following proposition true or false? Justify your conclusion with a counterexample or a proof. For each integer a, 3 divides a + 23a. 20. Are the following statements true or false? Either prove the statement is true or provide a counterexample to show it is false. (a) For all integers a and b, if a · b = 0 (mod 6), then a = 0 (mod 6) or h- 0 (mod 6)
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