How can matrices be written in Latex with or without vertical lines?

[basty]

How do you write a matrix such as below image in Latex, in this forum?

 

[gsal]

Come on...did you even google it?

one result

 

[DrClaude]

Normally, the easiest way to write a matrix is to use the pmatrix environment:

\begin{pmatrix}
2 & 6 & 1 \\ 1 & 2 & -1 \\ 5 & 7 & -4
\end{pmatrix}

$$
\begin{pmatrix}
2 & 6 & 1 \\ 1 & 2 & -1 \\ 5 & 7 & -4
\end{pmatrix}
$$

If you need the vertical line, you have to do the matrix "by hand," and it requires a bit more work:

\left(
\begin{array}{rrr|r}
2 & 6 & 1 & 7 \\ 1 & 2 & -1 & -1 \\ 5 & 7 & -4 & 9
\end{array}
\right)

$$
\left(
\begin{array}{rrr|r}
2 & 6 & 1 & 7 \\ 1 & 2 & -1 & -1 \\ 5 & 7 & -4 & 9
\end{array}
\right)
$$