Solutions to the system in Example IS are given as \begin{equation*} (x_1,\,x_2,\,x_3,\,x_4)=(-1-2a+3b,\,4+a-2b,\,a,\,b) \end{equation*} Evaluate the three equations of the original system with these expressions in $a$ and $b$ and verify that each equation is true, no matter what values are chosen for $a$ and $b$.