Matrix multiplication

sf1903 · #1 $Old$ November 7th, 2009, 09:40 AM

I need some guidance here...
$Name: MatrixMuliply.gif Views: 21 Size: 866 Bytes$
How do I multiply these three?

I only know how to multiply when it looks like this...
$Name: multply2.gif Views: 21 Size: 1.5 KB$
But I cant figure out how to do with the one above. Plz help

Defunkt · #2 $Old$ November 7th, 2009, 09:59 AM

Quote:

Originally Posted by sf1903 $View Post$

I need some guidance here...
Attachment 13728
How do I multiply these three?

I only know how to multiply when it looks like this...
Attachment 13729
But I cant figure out how to do with the one above. Plz help

Remember that $ABC = (AB)C = A(BC)$ . So you can either first multiply the first two and then multiply the result by the third, or first multiply the last two and then multiply the result by the first.

Prof Paulo · #3 $Old$ November 7th, 2009, 10:50 AM

Hi,

$\begin{pmatrix} 1 & 2 \end{pmatrix} \times \begin{pmatrix} 3 & 2\\ -1 & 0 \end{pmatrix}=\begin{pmatrix} 1 & 2 \end{pmatrix}$

Then you keep this result and multiply with the last matrix:

$\begin{pmatrix} 1 & 2 \end{pmatrix} \times \begin{pmatrix} 2 \\ 2 \end{pmatrix}=6$