# Thread: Matrices & char. polynomials.

1. ## Matrices & char. polynomials.

Where I could find a nice proof of following theorem:

A is matrix n x n over field F , similar to upper triangular matrix if and only if her characteristic polynomial can be factored into an expression with the form:
(x-t_1)(x-t_2)...(x-t_n)

2. Originally Posted by Also sprach Zarathustra
Where I could find a nice proof of following theorem:

A is matrix n x n over field F , similar to upper triangular matrix if and only if her characteristic polynomial can be factored into an expression with the form:
(x-t_1)(x-t_2)...(x-t_n)
$det(A)=(a_{11}-\lambda)A_{11}+\sum_{i=2}^{n}a_{i1}A_{i1}$

$(a_{11}-\lambda)A_{11}=(a_{11}-\lambda)(a_{22}-\lambda)...(a_{nn}-\lambda)$

$=(-1)^n\lambda^n+...+(-1)^{n-1}\lambda^{n-1}$

$p(0)=det(A)=\lambda_1\lambda_2...\lambda_n$
$(-1)^{n-1}=tr(A)=\sum_{i=1}^{n}\lambda_i$

$p(\lambda)=0$ has exactly n solutions $\lambda_1,...,\lambda_n$

$p(\lambda)=(\lambda_1-\lambda)(\lambda_2-\lambda)...(\lambda_n-\lambda)$

$p(0)=(\lambda_1)(\lambda_2)...(\lambda_n)=det(A)$