grandes-ecoles 2025 Q9

grandes-ecoles · France · polytechnique-maths__pc Matrices Determinant and Rank Computation

Let $A \in \mathrm{GL}_n(\mathbb{R})$ be an invertible matrix, and let $\mathbf{u}, \mathbf{v} \in \mathbb{R}^n$. Show more generally that $$\operatorname{det}\left(A + \mathbf{u v}^T\right) = \operatorname{det}(A)\left(1 + \left\langle \mathbf{v}, A^{-1} \mathbf{u} \right\rangle\right).$$

Let $A \in \mathrm{GL}_n(\mathbb{R})$ be an invertible matrix, and let $\mathbf{u}, \mathbf{v} \in \mathbb{R}^n$. Show more generally that
$$\operatorname{det}\left(A + \mathbf{u v}^T\right) = \operatorname{det}(A)\left(1 + \left\langle \mathbf{v}, A^{-1} \mathbf{u} \right\rangle\right).$$

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