5.71. Below is given a proof of a result. What result is proved? Proof Let a, b, Ce Z such that a² + b² = c². Assume, to the contrary, that a, b and c are all odd. By (the contrapositive of) Theorem 3.12 O, a? and b? are both odd. Therefore, a? = 2r +1 and b = 2s +1 for integers r and s. Thus, a? + b² = 2r + 2s + 2 = 2 (r + s+1). Since r + s+1 is an integer, a? + b is even. However, a? + b² = c² and c2 is odd. This is a contradiction.

Elements Of Modern Algebra
8th Edition
ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter6: More On Rings
Section6.1: Ideals And Quotient Rings
Problem 34E: 34. If is an ideal of prove that the set is an ideal of . The set is called the annihilator of the...
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5.71. Below is given a proof of a result. What result is proved?
Proof Let a, b, Ce Z such that a² + b² = c². Assume, to the contrary, that a, b and c are all odd. By (the contrapositive of) Theorem 3.12 O, a?
and b? are both odd.
Therefore, a? = 2r +1 and b = 2s +1 for integers r and s. Thus, a? + b² = 2r + 2s + 2 = 2 (r + s+1). Since r + s+1 is an integer,
a? + b is even. However, a? + b² = c² and c2 is odd. This is a contradiction.
Transcribed Image Text:5.71. Below is given a proof of a result. What result is proved? Proof Let a, b, Ce Z such that a² + b² = c². Assume, to the contrary, that a, b and c are all odd. By (the contrapositive of) Theorem 3.12 O, a? and b? are both odd. Therefore, a? = 2r +1 and b = 2s +1 for integers r and s. Thus, a? + b² = 2r + 2s + 2 = 2 (r + s+1). Since r + s+1 is an integer, a? + b is even. However, a? + b² = c² and c2 is odd. This is a contradiction.
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