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Cross product for parallel vectors

by adoado
Tags: cross, parallel, product, vectors
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Mar13-10, 08:11 PM
P: 72
1. The problem statement, all variables and given/known data

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

2. Relevant equations

3. 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?

Adrian ^^
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Mar13-10, 08:52 PM
HW Helper
P: 6,206
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.
Mar16-10, 02:49 AM
P: 72
Cheers, thanks for that. I got it all figured out now..


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