Question

Use the matrix method to solve:

x + 4y = 8

2x + y = 9

x=?
y=?

Answer 1

x=3.43 y=1.14

Answer 2

\[\left(\begin{array}{cc|c}1 & 4 & 8 \\ 2 & 1 & 9\end{array}\right)\]
Substract 2*row 1 from row 2:
\[\left(\begin{array}{cc|c}1 & 4 & 8 \\ 0 & -7 & -7\end{array}\right)\]
now multiply row 2 by -1/7:
\[\left(\begin{array}{cc|c}1 & 4 & 8 \\ 0 & 1 & 1\end{array}\right)\]
substract 4 * row 2 from row 1:
\[\left(\begin{array}{cc|c}1 & 0 & 4 \\ 0 & 1 & 1\end{array}\right)\]

x = 4, y = 1