Exercise 2.2.13

We have $\mathit{Ax}=b$, i.e. $\left[\begin{array}{cc}\hfill 1\hfill & \hfill 0\hfill \\ \hfill 1\hfill & \hfill 1\hfill \\ \hfill 1\hfill & \hfill 3\hfill \\ \hfill 1\hfill & \hfill 4\hfill \end{array}\right]\left[\begin{array}{c}\hfill x_1\hfill \\ \hfill x_2\hfill \end{array}\right]=\left[\begin{array}{c}\hfill 0\hfill \\ \hfill 8\hfill \\ \hfill 8\hfill \\ \hfill 20\hfill \end{array}\right]$, it we change the measurements to $p=1,5,13,17$, then we find $\widehat{x}=\left[\begin{array}{c}\hfill 1\hfill \\ \hfill 4\hfill \end{array}\right]$