grandes-ecoles 2023 QExercise-3

grandes-ecoles · France · polytechnique-maths__fui Matrices Determinant and Rank Computation
Let $J \in M_{n}(\mathbb{C})$ be the matrix defined by
$$J = \left( \begin{array}{ccccc} 0 & 1 & 0 & \ldots & 0 \\ 0 & 0 & 1 & \cdots & 0 \\ \vdots & \ddots & \ddots & \ddots & \vdots \\ \vdots & & \ddots & 0 & 1 \\ 1 & 0 & \ldots & 0 & 0 \end{array} \right).$$
Deduce the value of the determinant
$$\left| \begin{array}{ccccc} a_{0} & a_{1} & \ldots & a_{n-2} & a_{n-1} \\ a_{n-1} & a_{0} & \ddots & & a_{n-2} \\ \vdots & \ddots & \ddots & \ddots & \vdots \\ a_{2} & & \ddots & a_{0} & a_{1} \\ a_{1} & a_{2} & \cdots & a_{n-1} & a_{0} \end{array} \right|$$
where $a_{0}, \ldots, a_{n-1}$ are arbitrary complex numbers.
Let $J \in M_{n}(\mathbb{C})$ be the matrix defined by

$$J = \left( \begin{array}{ccccc} 
0 & 1 & 0 & \ldots & 0 \\
0 & 0 & 1 & \cdots & 0 \\
\vdots & \ddots & \ddots & \ddots & \vdots \\
\vdots & & \ddots & 0 & 1 \\
1 & 0 & \ldots & 0 & 0
\end{array} \right).$$

Deduce the value of the determinant

$$\left| \begin{array}{ccccc} 
a_{0} & a_{1} & \ldots & a_{n-2} & a_{n-1} \\
a_{n-1} & a_{0} & \ddots & & a_{n-2} \\
\vdots & \ddots & \ddots & \ddots & \vdots \\
a_{2} & & \ddots & a_{0} & a_{1} \\
a_{1} & a_{2} & \cdots & a_{n-1} & a_{0}
\end{array} \right|$$

where $a_{0}, \ldots, a_{n-1}$ are arbitrary complex numbers.