Let $A = (a_{ij})$ be an invertible $n\times n$ matrix. I wonder how to prove that $A$ is a product of elementary matrices. I suspect that we need to transform it into the identity matrix by using elementary row operations, but how to do it exactly?
P.S. I've checked questions which could be considered similar and neither of them deals with this exact (general) situation. Please don't mark this question as a duplicate unless you find a precise answer.
Best Answer
If A is an invertible nxn matrix, $A\bar x = \bar 0$ has only the trivial solution of $\bar 0$ because $$A^{-1}A\bar x = \bar x = A^{-1}\bar0 =\bar0 \tag{1}\label{1}$$ This implies A is a product of elementary matrices because it implies A is row equivalent to I
Let's assume the A is in REF, if one of the diagonal elements were $0$ we would have a row filled with $0$'s and would have more unknowns than equations (proof n>m implies nontrivial solution omitted) and as a consequence has a nontrivial solution. Therefore, since we have no nontrivial solution $\ref{1}$, I is the RREF of A and A is composed of elementary row operations of I