Math Is Fun Forum

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?

zetafunc

Moderator

Registered: 2014-05-21

Posts: 2,436

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

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)

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 48,421

Re: Vector multiplication

Hi MaxT,

Welcome to the forum!

Please see the links:

Dot Product

and

Cross Prduct.

---

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.

zetafunc

Moderator

Registered: 2014-05-21

Posts: 2,436

Website

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.

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

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!!

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.