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This may sound silly but I have a matrix with 4 rows and 3 columns. This matrix is labelled $A$.

The question says:

Find $m, n$ such that $A \in M_{m,n}(\Bbb R)$

Now is $m$ just 4 and $n$ is 3? Apologies if this is obvious, just wanted to make sure this was the correct notation since for example $a_{34}$ would denote the element in the third row and fourth column of a matrix.

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Your assertion is correct (and your $A$ does not posess an element $a_{34}$). Other notations include $$M_{m,n} (\mathbb R), \mathbb R^{m\times n}, \mathbb R^{(m,n)}, {\rm Mat}_{m,n}(\mathbb R)$$ And most of the time, $m$ is the number of rows and $n$ is the number of columns (not all the time, duh)

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  • $\begingroup$ Yes I know it does not possess that element, was just stating the fact. Thanks. $\endgroup$ – Ryan Oct 30 '13 at 18:53
  • $\begingroup$ @Ryan happy to have helped. If that solved the question for you, please mark it as solved to signal that no further input is needed. $\endgroup$ – AlexR Oct 30 '13 at 18:54
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$A\in M_{4,3}(\mathbb{R})$ and yes, for the second question.

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