\documentclass[12pt]{report}\usepackage[cp1251]{inputenc}
\usepackage[russian]{babel}
\usepackage{pscyr}\usepackage{colordvi}
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%%             Copyright (C) 1994 1999 David Carlisle          %%
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\usepackage{lscape}% см короткое упоминание об этом пакете в Гуссенс М., Миттельбах Ф., Самарин А.
                   % Путеводитель по LaTeX М.:Мир 1999 с. 109
                   % Стилевой файл lscape находится в директории tex/latex/graphics
                   % Обратный переключатель \endlandscape в книге не описан
                   % Результат поворота всегда виден в ps или даже в dvi, если правильно настроить Yap
\begin{document}

\begin{tabular}{|c|c|p{250pt}|}
\hline
A1 & A2 & Приравнивая нулю определитель полученной матрицы, записываем искомое условие нестабильности
$$
6(\ddot xx +y+\dot x)-(3\ddot x+2x+  3\dot x)(\ddot x+7\ddot y +4)=0.
$$
\\
b1 & b2 & $x$\\
\hline
\end{tabular}


\landscape
\begin{tabular}{|c|c|c|}
\hline
A1 & A2 & A3\\
b1 & b2 & b3\\
\hline
\end{tabular}

\endlandscape

\begin{tabular}{|c|c|c|}
\hline
$x^2+y^2$ & A2 & A3\\
b1 & b2 & b3\\
\hline
\end{tabular}



\end{document}