# Section7Unitary Matrices (NM, 18 Sep)¶ permalink

##### Definition7.1

A matrix $Q \in \Cmm$ is unitary if its columns form an orthogonal, orthonormal set.

It follows that $Q^{-1} =Q^\star\text{.}$

# Subsection7.1Exercise(s)

##### Exercise7.2(Exercise 2.1 of [2])

Show that if a matrix is both triangular and unitary, then it is diagonal.

Hint