Answer
$\begin{bmatrix}1&-4\\0&28\end{bmatrix}$
Work Step by Step
Given matrix is $\begin{bmatrix}1&-4\\7&0\end{bmatrix}$
Row transformation is $R_{2}=-7R_{1}+R_{2}$
The changed matrix is
$\begin{bmatrix}1&-4\\-7(1)+7&-7(-4)+0\end{bmatrix}=\begin{bmatrix}1&-4\\0&28\end{bmatrix}$
