Cross product for parallel vectors

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SUMMARY

The discussion centers on determining whether the line through points (4,1,-1) and (2,5,3) is parallel to the line through points (-3,2,0) and (5,1,4). The direction vectors calculated are A = (-2,4,4) and B = (8,-1,4). The conclusion reached is that the lines are not parallel, as the cross product A x B is not the zero vector, confirming that the vectors do not satisfy the condition for parallelism.

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Homework Statement



Is the line through (4,1,-1) and (2,5,3) parallel to the line through (-3,2,0) and (5,1,4)?

Homework Equations





The Attempt at a Solution



Line one 'direction' = (-2,4,4) = A
Line two 'direction' = (8,-1,4) = B

I remember that the cross product of two vectors is zero if they are parallel, but AxB is not the zero vector; the answer in the book says they are indeed parallel...

Is this not the right method?

Cheers,
Adrian ^^
 
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If they were parallel, you could write one direction as a scalar multiple of the other. Since you cannot do that as well as the cross-product is not zero, the vectors are not parallel.
 
Cheers, thanks for that. I got it all figured out now..

Thanks,
Adrian
 

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