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## #1 2023-01-09 00:19:15

MaxT
Member
Registered: 2023-01-09
Posts: 3

### Vector multiplication

Hello,
Can someone help me with basic vector multiplication please.
I understand (I think!) dot product (scalar result) and cross product (vector result), but I was watching a video where someone did this

writing this in the format of x axis, y axis...

vector a:  3, 1.5
vector b:  3, 5

and multiplied them as:

3 x 3 = 9
1.5 x 5 = 7.5

claiming  the result of multiplying the vectors was a vector: 9, 7.5

Is that right?

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## #2 2023-01-09 00:36:19

zetafunc
Moderator
Registered: 2014-05-21
Posts: 2,415
Website

### Re: Vector multiplication

Hi MaxT,

Welcome to the forum.

Almost -- the dot product of two vectors is a scalar, not a vector. In this case we need to add together the results, i.e.

9 + 7.5 = 16.5

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## #3 2023-01-09 00:43:17

MaxT
Member
Registered: 2023-01-09
Posts: 3

### Re: Vector multiplication

Yes - that's what I thought was right - a scalar of 16.5

So, is the operation I wrote out - which I saw someone else do - not a valid operation at all?
I didn't think it was but it left me confused.

Last edited by MaxT (2023-01-09 00:43:44)

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## #4 2023-01-09 00:43:24

ganesh
Registered: 2005-06-28
Posts: 41,293

### Re: Vector multiplication

Hi MaxT,

Welcome to the forum!

Dot Product

and

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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## #5 2023-01-09 01:30:35

zetafunc
Moderator
Registered: 2014-05-21
Posts: 2,415
Website

### Re: Vector multiplication

MaxT wrote:

Yes - that's what I thought was right - a scalar of 16.5

So, is the operation I wrote out - which I saw someone else do - not a valid operation at all?
I didn't think it was but it left me confused.

It's a perfectly valid operation, just that the answer should have been a scalar (rather than a vector), i.e.

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## #6 2023-01-09 02:06:21

MaxT
Member
Registered: 2023-01-09
Posts: 3

### Re: Vector multiplication

Yes - thank, I understand that.

The confusion was that the person in the video I watched GRAPHED that 9 + 7.5 result as a VECTOR!!

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## #7 2023-01-10 21:31:00

imcute
Member
Registered: 2022-09-28
Posts: 176

### Re: Vector multiplication

You cannot multiply two vectors like when you add them.
(it is correct in a CS perspective but not in a math perspective)
Dot product is what you was wanting to do.

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