• Support PF! Buy your school textbooks, materials and every day products Here!

Cross product for parallel vectors

  • Thread starter adoado
  • Start date
  • #1
72
0

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 ^^
 

Answers and Replies

  • #2
rock.freak667
Homework Helper
6,230
31
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.
 
  • #3
72
0
Cheers, thanks for that. I got it all figured out now..

Thanks,
Adrian
 

Related Threads for: Cross product for parallel vectors

Replies
2
Views
4K
  • Last Post
Replies
2
Views
757
  • Last Post
Replies
6
Views
827
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
5
Views
558
  • Last Post
Replies
5
Views
702
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
7
Views
1K
Top