Matrix/2/Square roots of identity matrix/Exercise

Find, appart from the matrices ${}{\begin{pmatrix}1&0\\0&1\end{pmatrix}}$ and ${}{\begin{pmatrix}-1&0\\0&-1\end{pmatrix}}$, four more matrices ${}M$ fulfilling the property

${}M^{2}={\begin{pmatrix}1&0\\0&1\end{pmatrix}}$.

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