Why is DB + CA^T - 2A undefined if only some terms are defined?

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ivykink
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Homework Statement



DB+CA^T-2A

D=3row x 3col
B=2x2
C=2row X 3col
A=3row X 2col


The Attempt at a Solution



It is my understanding that a row of a matrix is horizontal variables and a column is the vertical variables. And for multiplication of two matrices you need the colums of the first matrix to be equal to the number of rows in the second matrix.

so DB= (D3x3)x(A2x2) so therefore DB is undefined.

The transpose of A3x2->A2x3 so CA^T = (C2x3) x (A2x3) Which is also undefined.

So does this then mean that the answer for DB+CA^T-2A is just undefined or is the answer -2A? I am unsure what the answer is or how to word it correctly
 

Discussion

ivykink said:
It is my understanding that a row of a matrix is horizontal variables and a column is the vertical variables.
Yes, those elements.
And for multiplication of two matrices you need the colums of the first matrix to be equal to the number of rows in the second matrix.
Yes.
so DB= (D3x3)x(A2x2) so therefore DB is undefined.
Undefined.
The transpose of A3x2->A2x3 so CA^T = (C2x3) x (A2x3) Which is also undefined.
Undefined.
So does this then mean that the answer for DB+CA^T-2A is just undefined or is the answer -2A? I am unsure what the answer is or how to word it correctly
I'd say undefined.
 
Excellent thankyou, sorry if this was in the wrong area, I prob should of put it in math not eng.