Definition7.1
A matrix \(Q \in \Cmm\) is unitary if its columns form an orthogonal, orthonormal set.
A matrix \(Q \in \Cmm\) is unitary if its columns form an orthogonal, orthonormal set.
It follows that \(Q^{-1} =Q^\star\text{.}\)
Show that if a matrix is both triangular and unitary, then it is diagonal.
Hint