ThmDex – An index of mathematical definitions, results, and conjectures.
Determinant of a scaled complex matrix
Formulation 0
Let $A \in \mathbb{C}^{N \times N}$ be a D6159: Complex square matrix such that
(i) $\lambda \in \mathbb{C}$ is a D1207: Complex number
Then \begin{equation} \text{Det}(\lambda A) = \lambda^N \text{Det} A \end{equation}
Proofs
Proof 0
Let $A \in \mathbb{C}^{N \times N}$ be a D6159: Complex square matrix such that
(i) $\lambda \in \mathbb{C}$ is a D1207: Complex number
We have \begin{equation} \begin{split} \text{Det} (\lambda A) & = \sum_{\pi \in S_N} \left( \text{Sign}(\pi) \prod_{n = 1}^N \lambda A_{n, \pi(n)} \right) \\ & = \sum_{\pi \in S_N} \lambda^N \left( \text{Sign}(\pi) \prod_{n = 1}^N A_{n, \pi(n)} \right) \\ & = \lambda^N \sum_{\pi \in S_N} \left( \text{Sign}(\pi) \prod_{n = 1}^N A_{n, \pi(n)} \right) \\ & = \lambda^N \text{Det} A \\ \end{split} \end{equation}