ThmDex – An index of mathematical definitions, results, and conjectures.
F13071
Formulation 0
Let $A \in \mathbb{C}^{2 \times 2}$ be a D6159: Complex square matrix such that
(ii) $C_{i, j}$ is a D6183: Complex square matrix cofactor for $A$ with respect to $(i, j)$ for each $i, j \in \{ 1, 2 \}$
Let $i, j \in \{ 1, 2 \}$ each be a D5094: Positive integer.
Then
(1) \begin{equation} i = j \quad \implies \quad A_{i, 1} C_{j, 1} + A_{i, 2} C_{j, 2} = \text{Det} A \end{equation}
(2) \begin{equation} i = j \quad \implies \quad A_{1, i} C_{1, j} + A_{2, i} C_{2, j} = \text{Det} A \end{equation}
(3) \begin{equation} i \neq j \quad \implies \quad A_{i, 1} C_{j, 1} + A_{i, 2} C_{j, 2} = 0 \end{equation}
(4) \begin{equation} i \neq j \quad \implies \quad A_{1, i} C_{1, j} + A_{2, i} C_{2, j} = 0 \end{equation}