4. Z(G) = N Co(a). aEG
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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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Question
[Groups and Symmetries] How do you solve this question. Definitions are provided
![Center/Centralizer/Normalizer
Let G be a group.
• The center of G, denoted by Z(G), is the set of all elements in G that commute with
every element of G;
Z(G) = {g E G : gx = xg Vx € G}.
• Given an element a E G, the centralizer of a E G, denoted by CG(@), is the set of elements
in G that commute with a;
Cg(a) = {g € G : ga = ag}.
• If H 3 G, the centralizer of H in G, denoted by CG(H), is the set of elements in G that
commute with every element in H;
CG(H)= {g € G : gh = hg Vh E H}.
• If H < G, the normalizer of H in G is the set
NG(H)= {gE G : gHg = H}.
It follows by definition that G is Abelian if and only if Z(G) = G. Moreover, CG(G) = Z(G).
Theorem 2.27. Let G be a group. Then,
1. Z(G) < Cg(a) < G for all a E G.
2. Z(G) 3 CG(H)< Ng(H)<G for all H 3 G.
3. G is Abelian if and only if Z(G) = Cg(a) for all a E G.
4. Z(G) =
N Cala).
aEG](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F386e683b-b104-45bf-b231-5b109967da42%2F2e90aef0-19fb-4252-9130-d72bd18c2c43%2Ffzs7ga9_processed.png&w=3840&q=75)
Transcribed Image Text:Center/Centralizer/Normalizer
Let G be a group.
• The center of G, denoted by Z(G), is the set of all elements in G that commute with
every element of G;
Z(G) = {g E G : gx = xg Vx € G}.
• Given an element a E G, the centralizer of a E G, denoted by CG(@), is the set of elements
in G that commute with a;
Cg(a) = {g € G : ga = ag}.
• If H 3 G, the centralizer of H in G, denoted by CG(H), is the set of elements in G that
commute with every element in H;
CG(H)= {g € G : gh = hg Vh E H}.
• If H < G, the normalizer of H in G is the set
NG(H)= {gE G : gHg = H}.
It follows by definition that G is Abelian if and only if Z(G) = G. Moreover, CG(G) = Z(G).
Theorem 2.27. Let G be a group. Then,
1. Z(G) < Cg(a) < G for all a E G.
2. Z(G) 3 CG(H)< Ng(H)<G for all H 3 G.
3. G is Abelian if and only if Z(G) = Cg(a) for all a E G.
4. Z(G) =
N Cala).
aEG
![Question 3. Let
b
0 1
0 0
1
a
H =
c) : a, b, c e Q
1
under matrix multiplication. Notice that H is a group (you do not have to prove this).
(a) Find Z(H).
(b) Prove that Z(H)=Q, Q is under addition.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F386e683b-b104-45bf-b231-5b109967da42%2F2e90aef0-19fb-4252-9130-d72bd18c2c43%2Fp5pal8p_processed.png&w=3840&q=75)
Transcribed Image Text:Question 3. Let
b
0 1
0 0
1
a
H =
c) : a, b, c e Q
1
under matrix multiplication. Notice that H is a group (you do not have to prove this).
(a) Find Z(H).
(b) Prove that Z(H)=Q, Q is under addition.
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