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Is something like \(\begin{pmatrix} 3 \\ 7 \\ 2 \end{pmatrix} 4 \begin{pmatrix} 6 \\ 5 \\ 2 \end{pmatrix}=4 \begin{pmatrix} 3 \\ 7 \\ 2 \end{pmatrix} \begin{pmatrix} 6 \\ 5 \\ 2 \end{pmatrix}\)true?

 May 3, 2020
 #1
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A scalar will commute with a vector, which means, for example: 

 

 May 3, 2020
 #2
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to multiply two matrices the number of columns in the leftmost one has to be equal to the number of rows in the rightmost one, so you cant multiply two 3x1 vectors. if you have two square matrices their multiplication usually DOESNT commute

 May 3, 2020
 #3
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"... so you cant multiply two 3x1 vectors..."

 

This is true in mathematics.  Unfortunately, some pieces of software allow this.  For example, both SMath Studio and Mathcad produce the following:

 

 

I use Mathcad a lot, but this is a feature I'm not keen on!

Alan  May 3, 2020
 #4
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i think this is supposed to be the dot product

Guest May 3, 2020
 #5
avatar+30046 
+3

Yes, I guess they could be meant to be vectors in 3D Euclidean space. 

For two such vectors, u and v, the dot product is |u|.|v|.cos(theta), where theta is the angle between them.

Alan  May 3, 2020

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