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bham10246
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Homework Statement
Let [itex]G[/itex] be a group with a normal subgroup [itex]N[/itex] and subgroups [itex] K \triangleleft H \leq G. [/itex]
If [itex]H/K [/itex] is nontrivial, prove that at least one of [itex]HN/KN[/itex] and [itex](H\cap N)/(K\cap N)[/itex] must be nontrivial.
Homework Equations
The Three (or Four) Isomorphism Theorems.
The Attempt at a Solution
By the first isomorphism theorem, we saw that [itex]HN/KN \cong H/K [/itex]. So if [itex]H/K[/itex] is nontrivial, then [itex]HN/KN [/itex] is also nontrivial.
Now to show that [itex](H\cap N)/(K\cap N)[/itex] is also nontrivial, what normal subgroup of [itex]H/K [/itex] is this quotient group [itex](H\cap N)/(K\cap N)[/itex] isomorphic to?
Because of the "and" in the statement of the problem, should both be nontrivial?