Clear up some cross product confusion for me

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Discussion Overview

The discussion centers around the computation of the cross product of two vector expressions, A and B, defined in terms of other vectors (ro and r1). Participants express confusion regarding the application of the cross product when the components are not explicitly numerical but rather symbolic vectors.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents the vectors A and B in terms of other vectors and seeks clarification on how to compute A x B without numerical components.
  • Another participant suggests setting up a matrix to visualize the cross product, expressing uncertainty about the absence of a k component.
  • A claim is made that the cross product can be expressed as AXB = (x2 - y2)ro x r1, assuming x and y are scalars.
  • Discussion on the distributive law of cross products is introduced, with a participant questioning the simplification of terms like ro x ro and r1 x r1.
  • Participants explore the application of the distributive property to expand the cross product expression, leading to the identification of terms that simplify to zero.
  • One participant confirms the relationship r0 x r1 = -(r1 x r0) as a key point for further calculations.

Areas of Agreement / Disagreement

Participants generally agree on the properties of the cross product and the simplifications involved, but there is ongoing uncertainty regarding the application of these properties to the specific vector expressions presented.

Contextual Notes

Participants express confusion over the symbolic representation of vectors and the implications for calculating the cross product, indicating a need for clarity on the assumptions involved in their expressions.

2slowtogofast
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Here is what I have

A=xro+yr1

B=yro+xr1

I need to find A x B

I am confused about do it because The components of A and B are in terms of vectors

If A = 3i + 4j + 7k and B = 2i + 2j + 1k I would have no problem (these numbers are meaningless just giving an example) finding A x B but I don't have components I have vectors. Can some one explain how to do this. Thanks
 
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Could I set it up as follows

Sorry I don't no how to input a matrix hopefully this can get the idea across
ro r1 k ro r1
x y 0 x y
y x 0 y x

and then do the normal cross product thing where you multiply diagonals and so on. The thing that troubles me is there is really no k component. The only thing I know is my answer will be perpindicular to the plane with r0 and r1 so not sure what to do
 
AXB = (x2 - y2)r0Xr1.

I am assuming x and y are scalars.
 
hi 2slowtogofast! :smile:
2slowtogofast said:
Here is what I have

A=xro+yr1

B=yro+xr1

I need to find A x B


hints: distributive law

what are ro x ro and r1 x r1 ? :wink:
 
@tinytim

roxro = 0 I can see how that will simplify things I am confused about the distributive law part

A x (B+D) = (AxB)+(AxD)

I have somthing more like this

(xro+yr1) x (yro+xr1) = (xro+yr1) x yro + (xro+yr1) x xr1

Use the distributive rule again on the RHS

(xro x yro) + (yr1 x yro) + (xro x xr1) + (yr1 x r1)

Then the first and last terms are 0. Am on the right track or did I make a wrong turn somewhere
 
hi 2slowtogofast! :smile:

(just got up :zzz:)
2slowtogofast said:
(xro x yro) + (yr1 x yro) + (xro x xr1) + (yr1 x r1)

Then the first and last terms are 0. Am on the right track

yes :smile:

now what is the relationship between r1 x ro and ro x r1 ? :wink:
 
r0 x r1 = -(r1 x r0)

If that is correct i think i can take it from there thanks for the help
 
2slowtogofast said:
r0 x r1 = -(r1 x r0)

that's it! :smile:
 

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