# Math Help - determining matrix size

1. ## determining matrix size

Show that if A is an [m x n] matrix and A(BA) is defined, then B is an [n x m] matrix.

2. If A has order $m\times n$ look at BA first of all

For be BA to be defined B must have order $k\times m$ in turn BA must have order $k\times n$

Now for A(BA) to be defined $k=n$ therefore B has order $n\times m$

3. thank you, easy to understand when its right in front of me