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$\dfrac{a}{b} + \dfrac{1}{1+\dfrac{b}{a}}$ $\left(\dfrac{x^\frac{2}{5}}{y^\frac{3}{2}}\right)^{-2}\cdot \dfrac{(y^{-1}x^{-2})^{-\frac{1}{2}}}{(xy^2)^\frac{1}{10}}$ $s_x=\sqrt{{\frac{1}{n}} \big [(x_1-\overline{x})^2 + (x_2-\overline{x})^2 +\ldots + (x_n-\overline{x})^2 \big ]}$ $\sqrt{v+5}-\sqrt{v^2-7}=0$ $\sqrt[3]{v+5}-\sqrt[2]{v^2-7}=0$
$s_x=\sqrt{{\frac{1}{n}} \big [(x_1-\overline{x})^2 + (x_2-\overline{x})^2 +\ldots + (x_n-\overline{x})^2 \big ]}$

$s_x=\sqrt{{\frac{1}{n}} \big [(x_1-\overline{x})^2 + (x_2-\overline{x})^2 +\ldots + (x_n-\overline{x})^2 \big ]}$