# Geometric-harmonic mean

In mathematics, the geometric-harmonic mean M(x, y) of two positive real numbers x and y is defined as follows: we first form the geometric mean of x and y and call it g1, i.e. g1 is the square root of xy. We then form the harmonic mean of x and y and call it h1, i.e. h1 is the reciprocal of the arithmetic mean of the reciprocals of x and y.

Now we can iterate this operation with g1 taking the place of x and h1 taking the place of y. In this way, two sequences (gn) and (hn) are defined:

[itex]g_{n+1} = \sqrt{a_n g_n}[itex]

and

[itex]h_{n+1} = \frac{2}{\frac{1}{a_n} + \frac{1}{h_n}}[itex]

Both of these sequences converge to the same number, which we call the geometric-harmonic mean M(x, y) of x and y.

M(x, y) is a number between the geometric and harmonic mean of x and y; in particular it is between x and y. If r > 0, then M(rx, ry) = r M(x, y).

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