\rbqquest{
Multiplication by $i$ has what effect on a number in the complex plane?
}

\rbqchoice{
\begin{enumerate}[a)]
\item\label{answer} It rotates the number around the origin by 90 degrees counterclockwise.
\item It rotates the number around the origin by 90 degrees clockwise.
\item It takes a number to the number pointing in the opposite direction with the same distance from the origin.
\item It reflects the number across the imaginary axis.
\item It reflects the number across the real axis.
\item None of the above.
\item I don't know.
\end{enumerate}
}
\rbqans{
Answer: (\ref{answer}).  

We compute: $i(a+bi) = -b+ai,$ which is rotated by 90 degrees
counterclockwise.

\begin{center}
  \includegraphics[width=.5\textwidth]{../Images/fig6_3_1.pdf}\\
\end{center}

For example, $i\cdot 1=i$ and $i\cdot i=-1$. 

\hbcom{It would be nice to have figures for these two examples.}
}