# Math Help - Set Multiplication

1. ## Set Multiplication

Im going over old material of mine and cant remember how to multiply simple sets together. The sets I am trying to multiply together are {1,2,3} x {4,5}. Any anwsers would be very useful. Thanks Jon

2. Originally Posted by jonnysteals
Im going over old material of mine and cant remember how to multiply simple sets together. The sets I am trying to multiply together are {1,2,3} x {4,5}. Any anwsers would be very useful. Thanks Jon
I have never heard of set multiplication before. Maybe someone else at this forum has. Are you sure you didn't intend to do a form of matrix multiplication,

$\left(\begin{array}{c}1\\2\\3\end{array}\right)\ti mes\left(\begin{array}{cc}4&5\end{array}\right)\ =\ \left(\begin{array}{cc}
4&5\\
8&10\\
12&15
\end{array}\right)$

3. Originally Posted by jonnysteals
trying to multiply together are {1,2,3} x {4,5}.
Usually that notation is for ‘cross products (Cartesian Products)’.
$\left\{ {1,2,3} \right\} \times \left\{ {4,5} \right\} = \left\{ {\left( {1,4} \right),\left( {2,4} \right),\left( {3,4} \right),\left( {1,5} \right),\left( {2,5} \right),\left( {3,5} \right)} \right\}.$

4. Aha, all different combinations one from each set. I have to read more courses.

5. Yea if I had to guess thats what I would have guessed but I figured Id ask the more knowledge people on these boards. Thanks Jon. You guys respond very quick; I'm Impressed!.

6. Hello, Jon!

The sets I am trying to multiply together are {1,2,3} x {4,5}.

As I recall, set multiplication doesn't involve arithmetic, just pairing.

$\{1,2,3\} \times \{4,5\} \;=\;\{(1,4),\,(1,5),\,(2,4),\,(2,5),\,(3,4),\,(3, 5)\}$

You see, set multiplication can be performed with sets like:
. . $\{\text{shoes},\text{ ships},\text{ sealing wax}\}$ and $\{\text{cabbages},\text{ kings}\}$