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Root-mean-square

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The root-mean-square or quadratic mean of a collection of real numbers x_1,\dots , x_n is defined to be \sqrt{\frac{x^2_1+x^2_2+\dots+x^2_n}{n}}. This is the second power mean of the x_i.

It is so-named because it is the square root of the mean of the squares of the x_i.

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