Jambmaths question:
Evaluate $\left| \begin{matrix} -1 & -1 & -1 \\ 3 & 1 & -1 \\ 1 & 2 & 1 \\\end{matrix} \right|$
Option A:
–12
Option B:
–4
Option C:
4
Option D:
–2
Jamb Maths Solution:
$\begin{align} & \left| \begin{matrix} -1 & -1 & -1 \\ 3 & 1 & -1 \\ 1 & 2 & 1 \\\end{matrix} \right|=-1\left| \begin{matrix} 1 & -1 \\ 2 & 1 \\\end{matrix} \right|-(-1)\left| \begin{matrix} 3 & -1 \\ 1 & 1 \\\end{matrix} \right|-1\left| \begin{matrix} 3 & 1 \\ 1 & 2 \\\end{matrix} \right| \\ & =-1(1+2)+1(3+1)-1(6-1) \\ & =-3+4-5=-4 \end{align}$
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