\documentclass[a4paper,12pt]{article}
\usepackage{epsfig}
\newcommand{\un}{\underline}
\begin{document}
\parindent=0pt


\begin{center}
\textbf{Vector Fields}

\textit{\textbf{Scalar and Vector Fields}}
\end{center}

\textbf{Question}

Sketch the following plane vector field and determine its field
lines.

$\un{F}(x,y) = e^x \un{i} + e^{-x} \un{j}$


\textbf{Answer}

$\begin{array}{l}
\textrm{The field lines satisfy }\frac{dx}{e^x} = \frac{dy}{e^{-x}}\\
\rm{Thus \ } \frac{dy}{dx}=e^{-2x}.\\
\textrm{The field lines are the curves}\\
y = -\frac{1}{2} e^{-2x} + C.
\end{array}
\ \ \ \ \
\begin{array}{c}
\epsfig{file=VF-1A-5.eps, width=40mm}
\end{array}$

\end{document}