Answer:
![\left[\left.\begin{matrix}1 & 0 & 0\\ 0 & 6 & 0\\ 0 & 0 & 7\end{matrix}\right|\begin{matrix}7\\ 5\\ 5\end{matrix}\right]](https://tex.z-dn.net/?f=%5Cleft%5B%5Cleft.%5Cbegin%7Bmatrix%7D1%20%26%200%20%26%200%5C%5C%200%20%26%206%20%26%200%5C%5C%200%20%26%200%20%26%207%5Cend%7Bmatrix%7D%5Cright%7C%5Cbegin%7Bmatrix%7D7%5C%5C%205%5C%5C%205%5Cend%7Bmatrix%7D%5Cright%5D)
Step-by-step explanation:
The given augmented matrix is
![\left[\left.\begin{matrix}3 & 0 & 0\\ 0 & 6 & 0\\ 0 & 0 & 7\end{matrix}\right|\begin{matrix}21\\ 5\\ 5\end{matrix}\right]](https://tex.z-dn.net/?f=%5Cleft%5B%5Cleft.%5Cbegin%7Bmatrix%7D3%20%26%200%20%26%200%5C%5C%200%20%26%206%20%26%200%5C%5C%200%20%26%200%20%26%207%5Cend%7Bmatrix%7D%5Cright%7C%5Cbegin%7Bmatrix%7D21%5C%5C%205%5C%5C%205%5Cend%7Bmatrix%7D%5Cright%5D)
Here, we need to perform the row operation 
and replace 
in the above matrix.
So, divide each element of in the given matrix and other elements remain same.
![\left[\left.\begin{matrix}\dfrac{3}{3} & \dfrac{0}{3} & \dfrac{0}{3}\\ 0 & 6 & 0\\ 0 & 0 & 7\end{matrix}\right|\begin{matrix}\dfrac{21}{3}\\ 5\\ 5\end{matrix}\right]](https://tex.z-dn.net/?f=%5Cleft%5B%5Cleft.%5Cbegin%7Bmatrix%7D%5Cdfrac%7B3%7D%7B3%7D%20%26%20%5Cdfrac%7B0%7D%7B3%7D%20%26%20%5Cdfrac%7B0%7D%7B3%7D%5C%5C%200%20%26%206%20%26%200%5C%5C%200%20%26%200%20%26%207%5Cend%7Bmatrix%7D%5Cright%7C%5Cbegin%7Bmatrix%7D%5Cdfrac%7B21%7D%7B3%7D%5C%5C%205%5C%5C%205%5Cend%7Bmatrix%7D%5Cright%5D)
Therefore, the required matrix is .
