take the coefients and use gausian elimination [tex] \left[\begin{array}{ccc}-1&4&|8\\-2&1&|9\end{array}\right] [/tex] multiply top row by -2 and add to 2nd row [tex] \left[\begin{array}{ccc}-1&4&|8\\0&-7&|-7\end{array}\right] [/tex] divide bottom row by -7 [tex] \left[\begin{array}{ccc}-1&4&|8\\0&1&|1\end{array}\right] [/tex] multiply bottom row by -4 and add to top row [tex] \left[\begin{array}{ccc}-1&0&|4\\0&1&|1\end{array}\right] [/tex] times top row by -1 [tex] \left[\begin{array}{ccc}1&0&|-4\\0&1&|1\end{array}\right] [/tex]
