Test Index

JAMB Mathematics 2019 Paper

© africaexams.com

Question : 23

Total: 73

If

\begin{vmatrix} 2 & -4 \\ x & 9 \end{vmatrix} = 58

, find the value of x.

10
30
14
28

Solution:

Concept:

The determinant of a

2 \times 2

matrix

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

is

ad - bc

.

Explanation:

Given

\begin{vmatrix} 2 & -4 \\ x & 9 \end{vmatrix} = 58

.

Using the determinant formula, multiply

2

by

9

, then subtract

(-4)

multiplied by

x

.

(2 \times 9) - (-4 \times x) = 58

18 + 4x = 58

Subtract

18

from both sides:

4x = 58 - 18 = 40

Divide both sides by

4

:

x = \frac{40}{4} = 10

Answer:

x = 10

, so the correct option is A.

© africaexams.com

Go to Question:

Prev Question

Next Question