About the square of orthogonal matrices [closed]
Consider the matrix
$$Q=\begin{pmatrix}1&1\\-2&-1\end{pmatrix}$$
Clearly, $Q$ is not orthogonal, but
$$Q^2=\begin{pmatrix}-1&0\\0&-1\end{pmatrix}$$
is orthogonal.
Consider the matrix
$$Q=\begin{pmatrix}1&1\\-2&-1\end{pmatrix}$$
Clearly, $Q$ is not orthogonal, but
$$Q^2=\begin{pmatrix}-1&0\\0&-1\end{pmatrix}$$
is orthogonal.