# DOT Product

• Jul 20th 2006, 08:24 AM
kwtolley
DOT Product
The dot product [3 1 4]dot 2
-1
5 is.

My answer is 25, but I'm not sure. Thanks for any help given.
• Jul 20th 2006, 10:09 AM
CaptainBlack
Quote:

Originally Posted by kwtolley
The dot product [3 1 4]dot 2
-1
5 is.

My answer is 25, but I'm not sure. Thanks for any help given.

The dot product of two vectors $[x_1,\ x_2,\ x_3]$ and $[x_1,\ x_2,\ x_3]$ is:

$
\bold{x}\cdot \bold{y}=\sum_{i=1}^3 x_i y_i = x_1y_1+x_2y_2+x_3y_3
$
.

In this case we have $\bold{x}=[3,1,4]$ and $\bold{y}=[2,-1,5]$, so:

$
\bold{x}\cdot \bold{y}= 3\times 2+1\times (-5)+4\times 5=21
$
.

RonL
• Jul 20th 2006, 10:19 AM
kwtolley
thank you
I really needed help on that one. I was way off on seting it up. thanks again for checking
• Jul 20th 2006, 12:43 PM
topsquark
Quote:

Originally Posted by CaptainBlack
In this case we have $\bold{x}=[3,1,4]$ and $\bold{y}=[2,-1,5]$, so:

$
\bold{x}\cdot \bold{y}= 3\times 2+1\times (-5)+4\times 5=21
$
.

RonL

Hold on! There was a typo:

$\bold{x}\cdot \bold{y}= 3\times 2+1\times (-1)+4\times 5=25
$
.

So you were correct, ktwolley.

-Dan
• Jul 20th 2006, 01:21 PM
CaptainBlack
Quote:

Originally Posted by topsquark
Hold on! There was a typo:

$\bold{x}\cdot \bold{y}= 3\times 2+1\times (-1)+4\times 5=25
$
.

So you were correct, ktwolley.

-Dan

Opps, there you go, you should always check what a helper writes.
Hopefully they provide enough information that they have in fact done
what they say they are doing :o

RonL
• Jul 20th 2006, 08:59 PM
kwtolley
Its alllllll good
Thanks both of you. I check and recheck myself and other, but sometimes the problems are hard. Thanks again you guys here are a big help.