My Math Forum vector problems

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 May 23rd, 2012, 11:25 PM #1 Member   Joined: Mar 2012 Posts: 81 Thanks: 0 vector problems http://i.imgur.com/j2jCo.jpg can someone help me with this, & how do you solve 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/(|B||C|) For 3. and 4., add vectors by adding components.
May 24th, 2012, 02:57 PM   #3
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Re: vector problems

Quote:
 Originally Posted by mathman 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/(|B||C|) For 3. and 4., add vectors by adding components.

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/(|B||C|), where |B| is compute like in 2. and |C| similarly.

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