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\newcommand\tg{\qopname\relax o{tg}}
\newcommand\cotg{\qopname\relax o{cotg}}

$x = a_1^2 + a_2^2 + a_3^2 + ... + a_n^2$

$\frac{a}{b} + \frac{1}{1+\frac{b}{a}}$

$\dfrac{a}{b} + \dfrac{1}{1+\dfrac{b}{a}}$

$\sqrt{v+5}-\sqrt{v^2-7}=0$

$\sqrt[3]{v+5}-\sqrt[2]{v^2-7}=0$

$\left(\dfrac{x^\frac{2}{5}}{y^\frac{3}{2}}\right)^{-2}\cdot \dfrac{(y^{-1}x^{-2})^{-\frac{1}{2}}}{(xy^2)^\frac{1}{10}}$

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

$\dfrac{\tg{(-\frac{\pi}{4})} \cdot{\cotg{(-\frac{\pi}{4})}}} {\sin{(-\frac{3}{2}\pi)} \cdot \cos{(-4\pi)}}$

$x \in A, A \subset B \subseteq C \supset D \supseteq D \ni y$

$\mathcal{ABCD}$

$\alpha + \beta + \gamma + \delta +\psi + \eta + \pi + \sigma + \rho = \Omega + \Delta + \Pi$

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