LaTeX Forum

\documentclass[a4 paper,11pt]{article}

\usepackage{amsmath}

\begin{document}

\begin{flalign}
\delta W_{int}(\tau)&=-\int_{x}{\int{A}{(\tau_{xy}\cdot\delta\gamma_{xy}+\tau_{xz}\cdot\delta\gamma_{xz})}\cdot dA} \cdot dx\nonumber\\
&=-\int_{x}{int_{A}{(\tau_{xy}\cdot(-(z-z_{M})-\frac{\partial\omega}{\partial y})\nonumber\\
&\quad+\tau_{xz}\cdot((y-y_{M})-\frac{\partial\omega}{\partial z})\cdot\delta\vartheta^{'})}\cot dA}\cdot dx\nonumber\\
&=-\int_{x}{M_{xp}\cdot\delta\vartheta^{'}}\cdot dx&
\end{flalign}

\end{document}

./main.tex:20: Missing } inserted.
<inserted text> 
                }
l.20 \end{flalign}