Question

If matrix $ A=\begin{vmatrix}1&2&-1\\ 3&4&5\\ 0&6&7\end{vmatrix} $ and its inverse is denoted by $ A^{-1}=\begin{vmatrix}a_{11}&a_{12}&a_{13}\\ a_{21}&a_{22}&a_{23}\\ a_{31}&a_{32}&a_{33}\end{vmatrix} $ , then the value of $ a_{23} $ is

• A. $ \frac{21}{20} $
• B. $ \frac{1}{5} $
• C. $ -\frac{2}{5} $
• D. $ \frac{2}{5} $

Answer 1

Answer: (C)

$|A|=-20$
$\therefore a_{23}=\frac{\text { Coractor }}{-20}=\frac{-8}{20}=\frac{-2}{5}$