<PRE><B>Question 209061</B>
Determine whether the points lie on a straight line
A(5,1,3), B(7,9,-1), C(1,-15,11)
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For A to B:
diffx = 2
diffy = 8
diffz = -4
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For A to C:
diffx = -4
diffy = -16
diffz = 8
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The differences have the same ratios, ie, the AC differences are -2 times the AB differences.  The 3 points are colinear.</PRE>