(d) Show that Theorem 1 does not hold for n 1 and n = 2. That is, show that the multiplicative groups Z and Z are cyclic. (e) The proof of Theorem 1 is thus currently incomplete, as it does not explicitly use the hypothesis that n > 3. In what parts of the proof is that assumption implicitly used?

Algebra & Trigonometry with Analytic Geometry
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ISBN:9781133382119
Author:Swokowski
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Chapter10: Sequences, Series, And Probability
Section: Chapter Questions
Problem 63RE
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please send handwritten solution for part d , e only handwritten solution accepted
We are now ready to prove Theorem 1:
Proof of Theorem 1. We know that an element kEZn belongs to Z if and only
if k and 2" are coprime, that is, if and only ifk is odd. In particular, the elements
a := 2"-1 –1 and b := 2"-1+ 1
belong to Z, and we have
a² = (2"-I - T)² :
2n x2n-2
+ T = T,
%3D
%3D
2n
and
(2"-1+1)2:
+ ī = T.
2n x2n-:
2n
Thus, Z contains at least two distinct elements of order 2. Since cyclic groups
contain at most one element of order 2 by Proposition 2, this implies that Z is
not cyclic.
Comprehension questions:
(a) Following the same approach as in the proof of Proposition 2, show that
for an integer m > 1, the additive group Zm either contains no element of
order 3 or contains exactly two elements of order 3.
(b) Explain how Proposition 3 can be used to show that the multiplicative
group Z is not cyclic.
(c) In the proof of Proposition 3, the following statement is not justified:
"However, since r is non-trivial, f(x) cannot have order 1."
Properly justify this statement.
(d) Show that Theorem 1 does not hold for = 1 and n 2. That is, show that
the multiplicative groups Z and Z are cyclic.
(e) The proof of Theorem 1 is thus currently incomplete, as it does not explicitly
use the hypothesis that n > 3. In what parts of the proof is that assumption
implicitly used?
Transcribed Image Text:We are now ready to prove Theorem 1: Proof of Theorem 1. We know that an element kEZn belongs to Z if and only if k and 2" are coprime, that is, if and only ifk is odd. In particular, the elements a := 2"-1 –1 and b := 2"-1+ 1 belong to Z, and we have a² = (2"-I - T)² : 2n x2n-2 + T = T, %3D %3D 2n and (2"-1+1)2: + ī = T. 2n x2n-: 2n Thus, Z contains at least two distinct elements of order 2. Since cyclic groups contain at most one element of order 2 by Proposition 2, this implies that Z is not cyclic. Comprehension questions: (a) Following the same approach as in the proof of Proposition 2, show that for an integer m > 1, the additive group Zm either contains no element of order 3 or contains exactly two elements of order 3. (b) Explain how Proposition 3 can be used to show that the multiplicative group Z is not cyclic. (c) In the proof of Proposition 3, the following statement is not justified: "However, since r is non-trivial, f(x) cannot have order 1." Properly justify this statement. (d) Show that Theorem 1 does not hold for = 1 and n 2. That is, show that the multiplicative groups Z and Z are cyclic. (e) The proof of Theorem 1 is thus currently incomplete, as it does not explicitly use the hypothesis that n > 3. In what parts of the proof is that assumption implicitly used?
We are now ready to prove Theorem 1:
Proof of Theorem 1. We know that an element kEZn belongs to Z if and only
if k and 2" are coprime, that is, if and only ifk is odd. In particular, the elements
a := 2"-1 –1 and b := 2"-1+ 1
belong to Z, and we have
a² = (2"-I - T)² :
2n x2n-2
+ T = T,
%3D
%3D
2n
and
(2"-1+1)2:
+ ī = T.
2n x2n-:
2n
Thus, Z contains at least two distinct elements of order 2. Since cyclic groups
contain at most one element of order 2 by Proposition 2, this implies that Z is
not cyclic.
Comprehension questions:
(a) Following the same approach as in the proof of Proposition 2, show that
for an integer m > 1, the additive group Zm either contains no element of
order 3 or contains exactly two elements of order 3.
(b) Explain how Proposition 3 can be used to show that the multiplicative
group Z is not cyclic.
(c) In the proof of Proposition 3, the following statement is not justified:
"However, since r is non-trivial, f(x) cannot have order 1."
Properly justify this statement.
(d) Show that Theorem 1 does not hold for = 1 and n 2. That is, show that
the multiplicative groups Z and Z are cyclic.
(e) The proof of Theorem 1 is thus currently incomplete, as it does not explicitly
use the hypothesis that n > 3. In what parts of the proof is that assumption
implicitly used?
Transcribed Image Text:We are now ready to prove Theorem 1: Proof of Theorem 1. We know that an element kEZn belongs to Z if and only if k and 2" are coprime, that is, if and only ifk is odd. In particular, the elements a := 2"-1 –1 and b := 2"-1+ 1 belong to Z, and we have a² = (2"-I - T)² : 2n x2n-2 + T = T, %3D %3D 2n and (2"-1+1)2: + ī = T. 2n x2n-: 2n Thus, Z contains at least two distinct elements of order 2. Since cyclic groups contain at most one element of order 2 by Proposition 2, this implies that Z is not cyclic. Comprehension questions: (a) Following the same approach as in the proof of Proposition 2, show that for an integer m > 1, the additive group Zm either contains no element of order 3 or contains exactly two elements of order 3. (b) Explain how Proposition 3 can be used to show that the multiplicative group Z is not cyclic. (c) In the proof of Proposition 3, the following statement is not justified: "However, since r is non-trivial, f(x) cannot have order 1." Properly justify this statement. (d) Show that Theorem 1 does not hold for = 1 and n 2. That is, show that the multiplicative groups Z and Z are cyclic. (e) The proof of Theorem 1 is thus currently incomplete, as it does not explicitly use the hypothesis that n > 3. In what parts of the proof is that assumption implicitly used?
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