Question

Evaluate the determinant for the following matrix: 1 4 4 5 2 2 1 5 5

Answer 1

A Laplace expansion along the first row gives

$\begin{vmatrix}1&4&4\\5&2&1\\1&5&5\end{vmatrix}=1\begin{vmatrix}2&1\\5&5\end{vmatrix}-4\begin{vmatrix}5&1\\1&5\end{vmatrix}+4\begin{vmatrix}5&2\\1&5\end{vmatrix}$
$=1(10-5)-4(25-1)+4(25-2)$
$=1$