Question

This matrix is singular.
\[\left[\begin{matrix}1 & 0 & 0 \\ 0 & -1 & 0\\ -1 & 2 & 0\end{matrix}\right]\]
you can see that the third row is a linear combination of the first and second rows:
(-1 x R1) + (-2 x R2)

I can't see that. that combination would get me \[\left(\begin{matrix}-1 \\ 2 \\ -3\end{matrix}\right)\]
and that is not the third column.

Answer 1

ok I confused column and rows

Answer 2

if you take the combination of -1*row1 and -2*row2
you get row3