Find y, if \(\begin{pmatrix}5 & -6 \\2 & -7\end{pmatrix}\begin{pmatrix}x \\ y \end{pmatrix} = \begin{pmatrix}7 \\-11\end{pmatrix}\)
A. 8
B. 5
C. 3
D. 2
Correct Answer: C
Explanation
\(\begin{pmatrix}5 & -6 \\2 & -7\end{pmatrix}\begin{pmatrix} x \\ y \end{pmatrix} = \begin{pmatrix}7 \\-11\end{pmatrix}\)
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
