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JAMB Mathematics 2014 Paper

Question : 20

Total: 47

Find y, if

\begin{pmatrix} 5 & -6 \\ 2 & -7 \end{pmatrix}\begin{pmatrix} x \\ y \end{pmatrix} = \begin{pmatrix} 7 \\ -11 \end{pmatrix}

Solution:

$\begin{pmatrix} 5 & -6 \\ 2 & -7 \end{pmatrix}\begin{pmatrix} x \\ y \end{pmatrix} = \begin{pmatrix} 7 \\ -11 \end{pmatrix}$

By matrices multiplication;

5x - 6y = 7 ........(1)

2x - 7y = -11 ......(2)

2 x (1): 10x - 12y = 14 .......(3)

5 x (2): 10x - 35y = -55 ......(4)

(3) - (4): 23y = 69

y = 69/23 = 3

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