JAMB 2011 · UTME · Q26

The inverse of matrix $N = \begin{pmatrix} 2 & 3 \\ 1 & 4 \end{pmatrix}$ is

Worked solution (try it first)

The determinant is $|N| = 2 \times 4 - 3 \times 1 = 5$ .
Swap the two diagonal entries (2 and 4) and change the signs of the other two: $\begin{pmatrix} 4 & -3 \\ -1 & 2 \end{pmatrix}$ .
Divide by the determinant: $N^{-1} = \frac15\begin{pmatrix} 4 & -3 \\ -1 & 2 \end{pmatrix}$ , option B.