May 23rd, 2012, 11:25 PM  #1 
Member Joined: Mar 2012 Posts: 81 Thanks: 0  vector problems 
May 24th, 2012, 12:14 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,770 Thanks: 700  Re: vector problems
1. I don't know how to draw something in 3 dimensions. For 2 and 5 you need to know about dot products. 2. B = ?(B.B) 5. cos? = B.C/(BC) For 3. and 4., add vectors by adding components. 
May 24th, 2012, 02:57 PM  #3  
Member Joined: Mar 2012 Posts: 81 Thanks: 0  Re: vector problems Quote:
for 4, i got ?3i+53j?16k , is that correct? and for 5, i find the dot value and thats it?  
May 24th, 2012, 03:26 PM  #4 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,948 Thanks: 1139 Math Focus: Elementary mathematics and beyond  Re: vector problems
4. A = 4i + 3j + 9k B = i + 8j  2k C = 14j  9k A  3C + B 4i + 3j + 9k  3(14j  9k) + i + 8j  2k = 3i + 11j + 7k  3(14j  9k) = 3i + 11j + 7k  42j + 27k = 3i  31j + 34k. 
May 25th, 2012, 12:45 PM  #5 
Global Moderator Joined: May 2007 Posts: 6,770 Thanks: 700  Re: vector problems
For 5. you need to divide by the magnitudes of the vectors to get the cos of the angle. B.C/(BC), where B is compute like in 2. and C similarly. 

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