I'm currently looking for the proof that a matrix $Q \in \mathbb{K}^{n\times n}$ that is unitary (i.e such that $QQ^*=I)$ is invertible and that $Q^* = Q^{-1}$.
2026-02-23 01:03:01.1771808581
Unitary matrices are invertible.
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A square matrix $A$ is called invertible if there exists $B$ such that $AB=I$, the identity matrix.
Compare this with the equation $QQ^*=I$ and conclude.