Matrix/2/Square roots of identity matrix/Exercise

Find, appart from the matrices $\left(\begin{array}{cc}1& 0\\ 0& 1\end{array}\right)$ and $\left(\begin{array}{cc}-1& 0\\ 0& -1\end{array}\right)$, four more matrices $M$ fulfilling the property $M^2=\left(\begin{array}{cc}1& 0\\ 0& 1\end{array}\right)$.

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