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$\begingroup$

How do you prove:

Given a finite group $G$, with $A,B$ subgroups then $$|AB|=\frac{|A||B|}{|A \cap B|}.$$

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    See [this post](http://math.stackexchange.com/questions/168942/order-of-a-product-of-subgroups) and other questions [linked there](http://math.stackexchange.com/questions/linked/168942)2016-07-19

2 Answers 2