\documentclass[12pt,twoside]{article}
\usepackage{russian,amssymb,amsmath}
\RequirePackage[discret]{correct}
\textwidth=160mm
\textheight=257mm
\oddsidemargin=4.6mm
\evensidemargin=4.6mm
\topmargin=-35mm
\parindent=7mm
\frenchspacing
\renewcommand{\baselinestretch}{1.71}
\hfuzz=0mm
\hoffset=-10mm
\voffset=7mm

\DeclareMathOperator{\Ln}{Ln}
\DeclareMathOperator{\Arcsin}{Arcsin}

\begin{document}

�⢥�, �ਢ������ � ���� ����筨��: $\Arcsin{z} = -i\Ln{(iz+\sqrt{1-z^2})},
\; \Arcsin{i} =2\pi k - i\ln{(\sqrt{2}-1)},\; k \in \mathbb{Z}$.

\end{document}

