\documentclass[a4paper,12pt]{article}
\newcommand\ds{\displaystyle}
\begin{document}

\parindent=0pt

QUESTION

Write $z=3j$ in exponential form.



ANSWER

\setlength{\unitlength}{.5in}
\begin{picture}(7,4)
\put(2.1,2.1){$\theta$} \put(2.1,3.5){$3j$} \put(1.7,1.7){O}
\put(0,2){\line(1,0){4}} \put(2,0){\line(0,1){4}}
\put(2,3.5){\circle*{.1}} \put(5,3){Clearly $\ds
r=3,\theta=\frac{\pi}{2}$} \put(5,2.3){Therefore
$3j=3e^{j\frac{\pi}{2}}$}
\end{picture}


\end{document}