\[ \text{How to solve a system equation?} \] \begin{align} x + 2y = 2 \tag{g} \\ 3x +4y = 2 \tag{f} \end{align}
\begin{equation} \begin{aligned} \text{Let solve the equation} \\ & x + 2y = 2 \label{3}\\ & \Rightarrow x = 2 - 2y \\ & \Rightarrow 3(2-2y) + 4y = 2 \\ & \Rightarrow 6 - 6y + 4y = 2 \\ & \Rightarrow 6 - 2y = 2 \\ & \Rightarrow \color{red}{y = 2} \\ & \text{ Sub }y = 2 \text{ into } x = 2-2y \\ & \Rightarrow x = 2 - 2 \times 2 \\ & \Rightarrow \color{red}{x = -2} \\ & \text{Therefore we have } \\ & \left[ \begin{array}{c} x \\ y \end{array} \right] = \left[ \begin{array}{c} -2 \\ 2 \end{array} \right] \\ \text{We can check our solution} \\ & -2 + 2(2) = 2 \\ & 3(-2) + 4(2) = 2 \end{aligned} \end{equation}