Question on: JAMB Mathematics - 2019

Given the matrix \(A = \begin{vmatrix} 3 & -2 \ 1 & 6 \end{vmatrix}\). Find the inverse of matrix A.

A

\(\begin{vmatrix} 6 & 2 \ 1 & 6 \end{vmatrix}\)

B

\(\begin{vmatrix} \frac{2}{11} & \frac{1}{12}\ \frac{3}{20} & \frac{1}{10} \end{vmatrix}\)

C

\(\begin{vmatrix} -3 & 2 \ -1 & -6 \end{vmatrix}\)

D

\(\begin{vmatrix} \frac{3}{10} & \frac{1}{10} \ \frac{-1}{20} & \frac{3}{20}\end{vmatrix}\)

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Correct Option: D

\(A = \begin{vmatrix} 3 & -2 \ 1 & 6 \end{vmatrix}\)

|A| = (3 x 6) - (-2 x 1)

= 18 + 2 = 20.

A\(^{-1}\) = \(\frac{1}{20} \begin{vmatrix} 6 & 2 \ -1 & 3 \end{vmatrix}\)

= \(\begin{vmatrix} \frac{6}{20} & \frac{2}{20} \ \frac{-1}{20} & \frac{3}{20} \end{vmatrix}\)

= \(\begin{vmatrix} \frac{3}{10} & \frac{1}{10} \ \frac{-1}{20} & \frac{3}{20} \end{vmatrix}\)

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