Arithmetic Mean-Geometric Mean Inequality
The Arithmetic Mean-Geometric Mean (AM-GM) Inequality states that the arithmetic mean of a set of positive real numbers is greater than or equal to the geometric mean of the same set of positive real numbers. For example, for the set 
, the Arithmetic Mean, 25, is greater than the Geometric Mean, 18; AM-GM guarantees this is always the case.
In general, AM-GM states that for a set of positive real numbers 
, the following always holds:
![$\displaystyle\left(\frac{a_1+a_2+\ldots+a_n}{n}\right)\geq\sqrt[n]{a_1a_2\cdots a_n}$](http://latex.artofproblemsolving.com/0/5/8/0581fd9f5352a22b848c414d9efaddc89ec8cd25.png)
The AM-GM inequalitiy is a specific case of the Power mean inequality. It (and the much more general Power Mean Inequality) are used fairly frequently to solve Olympiad-level Inequality problems, such as those on the USAMO and IMO.
