Jambmaths question:
Evaluate $\left| \begin{matrix} 4 & 2 & -1 \\ 2 & 3 & -1 \\ -1 & 1 & 3 \\\end{matrix} \right|$
Option A:
15
Option B:
55
Option C:
45
Option D:
25
Jamb Maths Solution:
$\begin{align} & \left| \begin{matrix} 4 & 2 & -1 \\ 2 & 3 & -1 \\ -1 & 1 & 3 \\\end{matrix} \right|=4\left| \begin{matrix} 3 & -1 \\ 1 & 3 \\\end{matrix} \right|-2\left| \begin{matrix} 2 & -1 \\ -1 & 3 \\\end{matrix} \right|-1\left| \begin{matrix} 2 & 3 \\ -1 & 1 \\\end{matrix} \right| \\ & \Delta =4(9+1)-2(6-1)-1(2+3) \\ & \Delta =40-10-5=25 \\\end{align}$
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