Can I show that y is in Ha\capKa?

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Homework Help Overview

The discussion revolves around subgroup properties in group theory, specifically exploring the intersection of cosets and subgroups. The original poster attempts to show that for subgroups H and K, the intersection of cosets Ha and Ka equals the coset of the intersection of the subgroups (H∩K)a.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the implications of elements belonging to the intersection of cosets and question the existence of certain elements within the groups. There is an exploration of the relationship between elements in Ha and Ka, and the conditions under which they belong to (H∩K)a.

Discussion Status

Participants are actively engaging with the problem, raising questions about the existence of elements and their relationships within the subgroups. Some guidance has been offered regarding the implications of elements being in both Ha and Ka, and the need to clarify the role of the element 'y' in the context of the problem.

Contextual Notes

There is an ongoing discussion about the notation and the implications of certain elements being in specific sets, with participants clarifying the conditions under which the statements hold true. The conversation reflects a collaborative effort to understand the underlying group theory concepts without reaching a definitive conclusion.

Punkyc7
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Let H and K be Subgroups
show Ha[itex]\cap[/itex]Ka = (H[itex]\cap[/itex]K)a for all a [itex]\in[/itex]G

pf

Let x[itex]\in[/itex]Ha[itex]\cap[/itex]Ka

Then x[itex]\in[/itex]Ha and x[itex]\in[/itex]Ka

Can I just say that x [itex]\in[/itex](H[itex]\cap[/itex]K)a ? Or am I missing something.
 
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hi Punkyc7! :smile:
Punkyc7 said:
Let x[itex]\in[/itex]Ha[itex]\cap[/itex]Ka

Then …

nooo :redface:

your next word should be "∃" :wink:
 
huh?
 
sorry, that character doesn't show up on some computers :redface:

your next words should be "there exists a y such that …" :smile:
 
Ok so there exist a y such that y is in Ha and Ka. Then is it right?
 
Punkyc7 said:
Ok so there exist a y such that y is in Ha and Ka. Then is it right?

no!

x is in Ha and Ka, so there exists a y in … such that … ? :smile:
 
bear with me..

There exist a y in (H[itex]\cap[/itex]K)a such that x=ya?
 
not quite

read it and try again :smile:
 
is it a y in G? such that x=ya? Then I am not sure if I need the a anymore.
 
  • #10
Punkyc7 said:
is it a y in G? such that x=ya?

no!

once again :smile:
 
  • #11
ok I am sure where the y is floating around but if its not in G or (H[itex]\cap[/itex]k)a. The only place left would have to be just H[itex]\cap[/itex]K right
 
  • #12
yes! :smile:

now, can you see why?
 
  • #13
suppose y is in both Ha and Ka.

what does this mean?

it means y = ha, for some h in H, and y = ka, for some k in K.

for this h, and this k:

ha = ka.

can you think of something to do with this? (perhaps multiply both sides by something?)

*****

that is only HALF the problem, though. the other half means you suppose:

y is in (H∩K)a.

what can you do with this?
 

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