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JAMB Mathematics 2023 Paper

Question : 19

Total: 80

If D =

\begin{bmatrix}2 & -1 & 3 \\ 4 & 1 & 2 \\ 1 & -3 & 1\end{bmatrix}

\| D \|

Solution:

$\begin{bmatrix}2 & -1 & 3 \\ 4 & 1 & 2 \\ 1 & -3 & 1\end{bmatrix}$

= 2[(1 x 1) - (2 x -3)] - (-1)[(4 x 1) - (2 x 1)] + 3[(4 x -3) - (1 x 1)]

= 2(1 - (-6)) + 1(4 - 2) + 3(-12 - 1)

= 2(1 + 6) + 1(2) + 3(-13)

= 2(7) + 1(2) + 3(-13)

= 14 + 2 - 39

∴ |D| = -23

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