Find, appart from the matrices ( 1 0 0 1 ) {\displaystyle {}{\begin{pmatrix}1&0\\0&1\end{pmatrix}}} and ( − 1 0 0 − 1 ) {\displaystyle {}{\begin{pmatrix}-1&0\\0&-1\end{pmatrix}}} , four more matrices M {\displaystyle {}M} fulfilling the property M 2 = ( 1 0 0 1 ) {\displaystyle {}M^{2}={\begin{pmatrix}1&0\\0&1\end{pmatrix}}} .
