March 23rd, 2012, 03:32 PM  #1 
Newbie Joined: Mar 2012 Posts: 1 Thanks: 0  Vector Question
Hi I was wondering how I could go about doing the following question: Three of the following represent the same line. Which one DOES NOT? a) x = (0,0,2) + t(2,6,2) b) x = (1,2,3) + t(2,6,2) c) x = (1,2,3) + t(1,3,1) d) x = (2,5,4) + t(1,3,1) and the reasoning behind it? I have a few questions but I'm not sure I can post more than one at a time. Thank you! 
March 23rd, 2012, 03:43 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,770 Thanks: 700  Re: Vector Question
All 4 lines are in the same direction, so the question is which 3 have at least one point in common. Start by noticing b) and c) have the same start, so these must be 2 of the vectors. Now take the differences between starts (b vs. a or b vs. d) and see which are in the same direction as the common direction. You can see that the d)  b) start works, while the a)  b) does not.


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