# Matrix multiplication doubt

• Oct 10th 2012, 02:45 AM
rcty
Matrix multiplication doubt
I have to do a matrices operation given as A.X=B where A is an 1X1 matrix, x is a 3X1 matrix and B is a 3X3 matrix with elements of 3rd column zero. here A is unknown term and i wish to find the value of A. please guide me on how to solve this problem?
• Oct 10th 2012, 04:27 AM
alane1994
Re: Matrix multiplication doubt
Are there any numbers with this? Or is this all purely hypothetical/theoretical?
Anywho... what you would do is you would take the B matrix, and then multiply it by the inverse of the X matrix to solve for A matrix. Seeing as it is sort a complicated process and rather awkward to put into words, I have a link that takes you to a great website that explains it better.
Matrix Inversion: Finding the Inverse of a Matrix
It is really a rather easy process. If you have questions, feel free to ask. I can break it down step by step if you wish.
• Oct 10th 2012, 08:24 AM
Soroban
Re: Matrix multiplication doubt
Hello, rcty!

Are you sure you have typed the problem correctly?

Quote:

$\displaystyle \text{I have to do a matrix operation: }\:A\cdot X\:=\:B$
$\displaystyle \text{where }A\text{ is a }1\!\times\!1\text{ matrix, }X\text{ is a }3\!\times\!1\text{ matrix,}$
$\displaystyle \text{and }B\text{ is a }3\!\times\!3\text{ matrix with elements of 3rd column zero..}$

$\displaystyle \text{I wish to find the value of }A.$

Do you realize what you are asking?

$\displaystyle \text{The equation is: }\:\begin{bmatrix}a\end{bmatrix}\cdot \begin{bmatrix}x_1 \\ x_2 \\ x_3 \end{bmatrix} \;=\; \begin{bmatrix}b_1&b_2&0 \\ b_3 &b_4 & 0 \\ b_5&b_6&0 \end{bmatrix}$

First of all, you cannot multiply a $\displaystyle [1\!\times\!1]$ by a $\displaystyle [3\!\times\!1]$

Even if you could, you wouldn't get a $\displaystyle [3\!\times\!3].$