Answer to Question #138330 in Abstract Algebra for J

Question #138330
Assume that (G,*) is a group and that (H,*) and (K,*) are subgroups of (G,*).Prove that (H intersects K , *) is a subgroup of (G,*)
1
Expert's answer
2020-10-14T18:09:56-0400

Let a,bHKa,b\in H\cap K. Then a,bHa,b\in H and a,bKa,b\in K. Since (H,)(H,*) and (K,)(K,*) are subgroups of

(G,)(G,*), abHa*b\in H and abKa*b\in K. By analogy for the inverse element a1a^{-1} of the element aa in group GG we have that a1Ha^{-1}\in H and a1Ka^{-1}\in K. Therefore, ab,a1HK.a*b, a^{-1}\in H\cap K. So, we conclude that (HK,)(H\cap K, *) is a subgroup of (G,).(G,*).


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