Problems in Group Theory (factor groups, etc)?

I'm having trouble with finding a way to figure out what factor groups are isomorphic to. In certain cases, there seems to be a 'formula' to figure it out (Z/nZ isomorphic to Zn), but all the examples in my textbook seem to be doing something different each time. Does anyone know how this should be... show more I'm having trouble with finding a way to figure out what factor groups are isomorphic to.
In certain cases, there seems to be a 'formula' to figure it out (Z/nZ isomorphic to Zn), but all the examples in my textbook seem to be doing something different each time.
Does anyone know how this should be done?

And in general, does anyone know a site that tells you how to do various other problems in group theory?
(My textbook is really bad, and usually doesn't show any examples of how to do what's asked in the practice problems, so I've been guessing at what I should be doing to figure things out).

Thanks!
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