RREF of $$$\left[\begin{array}{ccc}3 & 1 & 3\\1 & 7 & 1\\3 & 1 & 3\end{array}\right]$$$

Find the reduced row echelon form of $$$\left[\begin{array}{ccc}3 & 1 & 3\\1 & 7 & 1\\3 & 1 & 3\end{array}\right]$$$.

Divide row $$$1$$$ by $$$3$$$: $$$R_{1} = \frac{R_{1}}{3}$$$.

$$$\left[\begin{array}{ccc}1 & \frac{1}{3} & 1\\1 & 7 & 1\\3 & 1 & 3\end{array}\right]$$$

Subtract row $$$1$$$ from row $$$2$$$: $$$R_{2} = R_{2} - R_{1}$$$.

$$$\left[\begin{array}{ccc}1 & \frac{1}{3} & 1\\0 & \frac{20}{3} & 0\\3 & 1 & 3\end{array}\right]$$$

Subtract row $$$1$$$ multiplied by $$$3$$$ from row $$$3$$$: $$$R_{3} = R_{3} - 3 R_{1}$$$.

$$$\left[\begin{array}{ccc}1 & \frac{1}{3} & 1\\0 & \frac{20}{3} & 0\\0 & 0 & 0\end{array}\right]$$$

Multiply row $$$2$$$ by $$$\frac{3}{20}$$$: $$$R_{2} = \frac{3 R_{2}}{20}$$$.

$$$\left[\begin{array}{ccc}1 & \frac{1}{3} & 1\\0 & 1 & 0\\0 & 0 & 0\end{array}\right]$$$

Subtract row $$$2$$$ multiplied by $$$\frac{1}{3}$$$ from row $$$1$$$: $$$R_{1} = R_{1} - \frac{R_{2}}{3}$$$.

$$$\left[\begin{array}{ccc}1 & 0 & 1\\0 & 1 & 0\\0 & 0 & 0\end{array}\right]$$$

Since the element at row $$$3$$$ and column $$$3$$$ (pivot element) equals $$$0$$$, we need to swap the rows.

Find the first nonzero element in column $$$3$$$ under the pivot entry.

As can be seen, there are no such entries.

The reduced row echelon form is $$$\left[\begin{array}{ccc}1 & 0 & 1\\0 & 1 & 0\\0 & 0 & 0\end{array}\right]$$$A.