Ivan Shishkin, Rye (1878)

Problems/General algebraReviewed

Quotient of a group and subgroup

by Ancient Tree·
39
Difficulty scaleÉchelle de difficulté

This score reflects both the level of the required concepts and the difficulty of the solution.Ce score tient compte à la fois du niveau des notions nécessaires et de la difficulté de la résolution.

  1. 110First steps / middle schoolPremiers pas / collège
  2. 1125Beginner / high schoolDébutant / lycée
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Consider a group GG and a normal subgroup HH.
Is it necessarily the case that the quotient group G/HG/H is isomorphic to a subgroup of GG?

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Solution by Ancient Tree

Discussions0 useful votes

No, it is not necessarily the case. For example, with G=ZG=\mathbb{Z}, the subgroups of GG are of the form nZn\Z; but the quotients Z/nZ\Z /n\Z are not of this form since they are finite.

For a counter-example in the finite groups, it’s a bit less trivial.

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