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hzsh2009

铜虫 (小有名气)

[求助] 关于subgroup的证明

let H be a subgroup of order 2 in G.
Show that NG(H)= CG(H).  即normalzier和centralizer相等
Deduce that if NG(H)=G then H<=Z(G)
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zhencai688

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引用回帖:
4楼: Originally posted by zhencai688 at 2011-10-10 10:21:52:
Since N(G)/C(G)=Aut(Z2)=1,  N(G)=C(G).

Since NG(H)/CG(H)=Aut(H)=1,  NG(H)=CG(H).
5楼2011-10-10 10:25:37
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sdlmm

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【答案】应助回帖

★ ★
soliton923(金币+2): 鼓励参与讨论! 2011-09-28 22:58:01
hzsh2009(金币+10): 2011-09-29 05:18:43
Suppose H={e,y} be the order 2 subgp, then first easily we have C(H)<=N(H).Conversly, we have that for any x in N(H), xH=Hx={x, xy}={x,yx}, so we get xy=yx, i.e., x is in C(H). This implies that C(H)=N(H).
As to the second question, if N(H)=G, then this implies C(H)=G by the proof above, i.e., any element in G is commutative with y, that is y is in the center of G, this ends the proof.
2楼2011-09-28 13:34:25
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zhencai688

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soliton923: 您也可以写一个出来试一试哈~~^_^ 2011-09-28 22:58:29
引用回帖:
2楼: Originally posted by sdlmm at 2011-09-28 13:34:25:
Suppose H={e,y} be the order 2 subgp, then first easily we have C(H)<=N(H).Conversly, we have that for any x in N(H), xH=Hx={x, xy}={x,yx}, so we get xy=yx, i.e., x is in C(H). This implies that ...

证明的不错  方法很基本但很简练!
3楼2011-09-28 21:17:34
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zhencai688

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小雨萌萌(金币+1): 谢谢关注~ 2011-10-11 10:33:53
引用回帖:
3楼: Originally posted by zhencai688 at 2011-09-28 21:17:34:
证明的不错  方法很基本但很简练!

Since N(G)/C(G)=Aut(Z2)=1,  N(G)=C(G).
4楼2011-10-10 10:21:52
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