Answer
Solution set = $\{(x,y)\ \ | \ \ x=4-2y, \ \ y\in \mathbb{R}\}$
Work Step by Step
Reduce the augmented matrix $[A|B]$ to reduced row echelon form and interpret the result
$\left[\begin{array}{llll}
1 & 2 & | & 4\\
2 & 4 & | & 8
\end{array}\right]\rightarrow\left(\begin{array}{l}
.\\
R_{2}=r_{2}-2r_{1}
\end{array}\right)$
$\rightarrow\left[\begin{array}{llll}
1 & 2 & | & 4\\
0 & 0 & | & 0
\end{array}\right]$
The last equation is always true, the system is consistent (dependent).
Take $y\in \mathbb{R}.$
Equation 1 $\Rightarrow x=4-2y$
Solution set = $\{(x,y)\ \ | \ \ x=4-2y, \ \ y\in \mathbb{R}\}$
