Find the reduced row echelon form of this augmented matrix \( \left[\begin{array}{cccc}1 & -5 & 0 & 150 \\ 0 & 1 & 0 & 400 \\ 6 & -9 & 1 & 250\end{array}\right] \)
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To find the reduced row echelon form (RREF) of the given augmented matrix \[ \left[\begin{array}{cccc}1 & -5 & 0 & 150 \\ 0 & 1 & 0 & 400 \\ 6 & -9 & 1 & 250\end{array}\right], \] we can perform row operations. Let's denote the rows as \( R_1, R_2, R_3 \). 1. We start with the original matrix: \[ R_1 = \left[1, -5, 0, 150\right], \quad R_2 = \left[0, 1, 0, 400\right], \quad R_3 = \left[6, -9, 1, 250\right] \] 2. To eliminate the leading \(6\) in \(R_3\) (first column), we can subtract \(6 \times R_1\) from \(R_3\): \[ R_3' = R_3 - 6R_1 = \left[6, -9, 1, 250\right] - 6 \left[1, -5, 0, 150\right] = \left[6 - 6, -9 + 30, 1 - 0, 250 - 900\right] = \left[0, 21, 1, -650\right] \] 3. Now our matrix looks like this: \[ \left[\begin{array}{cccc}1 & -5 & 0 & 150 \\ 0 & 1 & 0 & 400 \\ 0 & 21 & 1 & -650\end{array}\right] \] 4. Next, we eliminate the \(21\) in \(R_3\) (second column) by subtracting \(21 \times R_2\) from \(R_3'\): \[ R_3'' = R_3' - 21R_2 = \left[0, 21, 1, -650\right] - 21\left[0, 1, 0, 400\right] = \left[0, 0, 1, -650 - 8400\right] = \left[0, 0, 1, -9050\right] \] 5. Now our matrix is: \[ \left[\begin{array}{cccc}1 & -5 & 0 & 150 \\ 0 & 1 & 0 & 400 \\ 0 & 0 & 1 & -9050\end{array}\right] \] 6. Now we will back substitute to clean up \(R_1\) by adding \(5 \times R_2\) to \(R_1\): \[ R_1' = R_1 + 5R_2 = \left[1, -5, 0, 150\right] + 5\left[0, 1, 0, 400\right] = \left[1, 0, 0, 150 + 2000\right] = \left[1, 0, 0, 2150\right] \] 7. Finally, we will also clean up \(R_2\) using the new \(R_1\): \[ R_2' = R_2 - 400R_3'' = \left[0, 1, 0, 400\right] - 0 = \left[0, 1, 0, 400\right] \] In the end, the matrix in reduced row echelon form is: \[ \left[\begin{array}{cccc}1 & 0 & 0 & 2150 \\ 0 & 1 & 0 & 400 \\ 0 & 0 & 1 & -9050\end{array}\right]. \] Thus, the RREF of the given augmented matrix is: \[ \left[\begin{array}{cccc}1 & 0 & 0 & 2150 \\ 0 & 1 & 0 & 400 \\ 0 & 0 & 1 & -9050\end{array}\right]. \]