Algebra
posted by mike .
Need to find the sizes of the product AB and the product BA whenever these exist. We are given A and B
A is 4 x 3, B is 3 x 6

I assume these are the sizes of matrices.
A is 4x3 meaning that there are 4 rows and 3 columns.
***
***
***
***
B is 3x4 meaning that there are 3 rows and 4 columns
####
####
####
A matrix product is meaningful (exists) if and only if the number of columns of the first matrix equals the number of rows of the second matrix, i.e.
Apq X Bqr = Cpr
While Bqr X Apq does not exist unless r=q.