[代數] 幾題關於group的證明@@

看板Math作者 (XD)時間14年前 (2011/10/17 00:26), 編輯推噓0(007)
留言7則, 2人參與, 最新討論串1/2 (看更多)
以下(G,*,e)為一群,想證 j -1 r j -j r (1) if a, b∈G, b*a*b = a , then b * a * b = a for some r∈N 這題想不出來啊...想用數學歸納法, k k+1 -(k+1) k -k -1 r 可是b *a*b 頂多拆b(b * a * b )b 然後中間卡一個a .... (2) │G│ is finite, H is a subset of G, prove that H is a subgroup of G if and only if e∈H and a*b∈H for all a, b∈G 不會證inverse∈H的部分@@ (3) H, K are subgroup of G, prove that if H∪K is a subgroup of G, then H⊆K or K⊆H -- -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 114.41.203.186

10/17 00:42, , 1F
第二題是for all a, b∈H吧?
10/17 00:42, 1F

10/17 00:46, , 2F
∵│G│is finite ∴{a^i}must be cyclic
10/17 00:46, 2F

10/17 00:47, , 3F
i.e. there is n∈N s.t. a^n = e
10/17 00:47, 3F

10/17 00:47, , 4F
pick a^(-1) = a^(n-1)
10/17 00:47, 4F

10/17 00:47, , 5F
note that a∈G
10/17 00:47, 5F

10/17 00:53, , 6F
對 是屬於H沒錯@@ 打錯
10/17 00:53, 6F

10/17 00:55, , 7F
感謝@@
10/17 00:55, 7F
文章代碼(AID): #1EcmMWDk (Math)
文章代碼(AID): #1EcmMWDk (Math)