need a help with 3d geometry

th3_r34p3r · December 15th, 2012, 08:02 PM

Find direction cosines of line perpendicular to lines with direction cosines proportional to (6,4,-4) and (-6,2,1).

skipjack · December 16th, 2012, 05:13 AM

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).

mathman · December 16th, 2012, 02:00 PM

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.

December 15th, 2012, 08:02 PM	#1
th3_r34p3r 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).
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December 16th, 2012, 05:13 AM	#2
skipjack Global Moderator Joined: Dec 2006 Posts: 20,380 Thanks: 2011	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).
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