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May 31st, 2017, 03:19 PM  #1 
Newbie Joined: May 2017 From: united kingdom Posts: 1 Thanks: 0  Vectors: where k is a scalar quantity Hello, I'd really appreciate some help with this particular question on vectors. The website is not offering answers. The question is: In the diagram above (not drawn to scale) X is the point on AB such that AX:XB=9:4. The position vector of A is 3a and the position vector of B is 3b. Find the value of k if OX=k(4a+9b) where k is a scalar quantity. Thanks so much! 
May 31st, 2017, 03:56 PM  #2 
Global Moderator Joined: Dec 2006 Posts: 20,972 Thanks: 2222 
k = 3/13

May 31st, 2017, 04:26 PM  #3 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,683 Thanks: 2664 Math Focus: Mainly analysis and algebra 
Find $\vec{AB}$. Then use $\vec{AX}=\frac9{13}\vec{AB}$ (why?). And finally $\vec{OX}=\vec{OA}+\vec{AX}$.

May 31st, 2017, 10:24 PM  #4 
Newbie Joined: Apr 2017 From: Bhadohi, U.P., India Posts: 26 Thanks: 1 
use of section formula: OX = [9(3a) + 4(3b)]/(9+4) = (9a+4b)3/13 

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