\left[\begin{array}{ccc}
1&0&0\\
0&\cos 180^\circ & \sin 180^\circ \\
0& \sin 180^\circ & \cos 180^\circ
\end{array}\right] = 
\left[\begin{array}{ccc}
1&0&0\\
0&-1&0\\
0&0&-1
\end{array}\right]