Writing equations with fractions and greek letters

Question

I'm trying to write this equation below and using the \usepackage{amsmath}, but I'm getting the error ! Argument of \frac has an extra } so I still don't know what I did wrong. And how can I make everything upright and not italic?

\begin{eqnarray}
\dot{\varepsilon} = A{\prime}{\prime}{\prime}\dot\frac{\sigma\dot\omega}{k\dotT}\dot\frac{1}{d^2}\left(1+\frac{\pi\dot\delta}{d}\dot\frac{D_{KG}}{D_v} \right)
\end{eqnarray}

Answer 1

You are using \dot to express a product; \dot is meant to put an accent (a dot) over its argument (as in the first \dot{\varepsilon}); for product you can use \cdot. Don't use eqnarray, but one of the environments provided by amsmath (align, for example). Since your example doesn't require any special alignment, I used a simple equation environment. \prime as a superscript requires ^; so you can write A^{\prime\prime\prime} or simply A'''.

Perhaps this is what you need:

\documentclass{report}
\usepackage{amsmath}

\begin{document}

\begin{equation}
\dot{\varepsilon} = A^{\prime\prime\prime}\cdot\frac{\sigma\cdot\omega}{k\cdot T}\cdot\frac{1}{d^2}\left(1+\frac{\pi\cdot\delta}{d}\cdot\frac{D_{KG}}{D_v} \right)
\end{equation}

\end{document}

Seeing the font used in the image attached to the question, it seems that the fourier packages was used:

\documentclass{report}
\usepackage{amsmath}
\usepackage{fourier}

\begin{document}

\begin{equation}
\dot{\othervarepsilon} = A'''\cdot\frac{\othersigma\cdot\Omega}{k\cdot T}\cdot\frac{1}{d^2}\left(1+\frac{\otherpi\cdot\otherdelta}{d}\cdot\frac{D_{KG}}{D_v} \right)
\end{equation}

\end{document}