Question

HElp Please its Pre-Calculus Matrix

Answer 1

The determinant is C. -541.

Using a cofactor expansion along the first row:

$\begin{vmatrix}-8&-4&-1\\1&7&-3\\8&9&9\end{vmatrix} = -8\begin{vmatrix}7&-3\\9&9\end{vmatrix} + 4\begin{vmatrix}1&-3\\8&9\end{vmatrix} - \begin{vmatrix}1&7\\8&9\end{vmatrix} \\\\= -8(7\times9-(-3)\times9) + 4(1\times9-(-3)\times8) - (1\times9-7\times8) \\\\ = -8(63+27) + 4(9+24) - (9-56)\\\\= \boxed{-541}$