調和平均
定義：Harmonic Mean
与えられた $n$ 個の数値の逆数の算術平均の逆数を調和平均という.\[H = \frac{n}{\frac{1}{x_1} + \frac{1}{x_2} + \cdots + \frac{1}{x_n}}\]
Mathematics is the language with which God has written the universe.
