5. \(\tan \theta < 0\)이고 \(\cos\left(\frac{\pi}{2} + \theta\right) = \frac{\sqrt{5}}{5}\)일 때, \(\cos \theta\)의 값은? [3점]

\begin{itemize}
    \item[1] \(-\frac{2\sqrt{5}}{5}\)
    \item[2] \(-\frac{\sqrt{5}}{5}\)
    \item[3] 0
    \item[4] \(\frac{\sqrt{5}}{5}\)
    \item[5] \(\frac{2\sqrt{5}}{5}\)
\end{itemize}