# Help with full rank factorization

#### learningstill

I've been tasked with proving the existence of a full rank factorization for an arbitrary m x n matrix, namely:

Let $\textit{A}$ $\in$ $\textbf{R}^{m x n}$ with $\textit{rank(A) = r}$ then there exist matrices $\textit{B}$ $\in$ $\textbf{R}^{m x r}$ and $\textit{C}$ $\in$ $\textbf{R}^{r x n}$ such that $\textit{A = BC}$. Furthermore $\textit{rank(A) = rank(B) = r}$.

I think I can prove the second property if I assume the first using $\it{rank(AB)}$ $\leq$ $\it{rank(A)}$ and $\it{rank(AB)}$ $\leq$ $\it{rank(B)}$.

I'd appreciate a push in the right direction. Thanks.

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#### fresh_42

Mentor
2018 Award
We have the following situation:
$$V_n \stackrel{C}{\twoheadrightarrow} V_n/\operatorname{ker}A \cong V_r \cong \operatorname{im}A \stackrel{B}{\rightarrowtail} V_m$$
which together $BC$ transform as $A$. We have split the domain of $A\, : \,V_n \longrightarrow V_m$ into $V_n \cong \operatorname{ker}A \oplus V_n/\operatorname{ker}A$ and the codomain in $\operatorname{im}A \oplus V_{m-r}\,.$

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