My Math Forum need a help with 3d geometry

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 December 15th, 2012, 08:02 PM #1 Newbie   Joined: Dec 2012 Posts: 1 Thanks: 0 need a help with 3d geometry Find direction cosines of line perpendicular to lines with direction cosines proportional to (6,4,-4) and (-6,2,1).
 December 16th, 2012, 05:13 AM #2 Global Moderator   Joined: Dec 2006 Posts: 20,757 Thanks: 2138 Find a vector, such as (2, 3, 6), that is perpendicular to (6, 4, -4) and (-6, 2, 1), then calculate ?(2˛ + 3˛ + 6˛) = 7. Dividing (2, 3, 6) by 7 gives (2/7, 3/7, 6/7).
December 16th, 2012, 02:00 PM   #3
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Re: need a help with 3d geometry

Quote:
 Originally Posted by th3_r34p3r Find direction cosines of line perpendicular to lines with direction cosines proportional to (6,4,-4) and (-6,2,1).
To get a vector perpendicular to two vectors, take the cross product of the two vectors.

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