proving the identity for subgroups.

376 Views Asked by At

What is the best way to prove that if a group is a subgroup of some other group? Or more precisely how to prove that they have common identity element?

1

There are 1 best solutions below

0
On BEST ANSWER

Let $e$ be the identity of $G$ and $e'$ be the identity of $H$.

Then $e'e'=e'$ in $H$.

This also holds in $G$ because the multiplication in $H$ is the restriction of the multiplication in $G$.

Multiplying by the inverse of $e'$ in $G$, we cancel $e'$ on both sides to get $e'=e$.