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JAMB Mathematics 2014 Paper

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Question : 21

Total: 47

If

\begin{vmatrix} -x & 12 \\ -1 & 4 \end{vmatrix} = -12

, find x.

-6
-2
3
6

Solution:

Concept:

The determinant of a

2 \times 2

matrix

\begin{vmatrix} a & b \\ c & d \end{vmatrix}

is

ad - bc

.

Explanation:

Apply the determinant formula to

\begin{vmatrix} -x & 12 \\ -1 & 4 \end{vmatrix}

.

This gives

(-x)(4) - (12)(-1) = -12

.

Simplify:

-4x + 12 = -12

.

Subtract

12

from both sides:

-4x = -24

.

Divide both sides by

-4

:

x = 6

.

Answer:

x = 6

, so the correct option is D.

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