\documentclass[12pt,russian]{article}
\usepackage[dvips]{graphics,graphicx}
\usepackage{amsmath,rotate}
\usepackage{epsfig}
\usepackage[english,russian]{babel}
\begin{document}
\begin{equation}
\begin{cases}
 \Vec{y}=\begin{pmatrix} y_1 \\ y_2 \end{pmatrix} \\
 \Vec{f}=\begin{pmatrix} (1-y_2^2)*y_1-y_2 \\ y_1
 \end{pmatrix}=\begin{pmatrix} f_1 \\ f_2 \end{pmatrix}
\end{cases}
\eqno(3)
\end{equation}
\end{document}
