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Home  >>  CBSE XII  >>  Math  >>  Three Dimensional Geometry
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Are the points (2, 3, 4), (-1, -2, 1), (5, 8, 7) collinear?

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  • If the direction ratios of two lines segements are proportional, then the lines ae parallel.
Given $ A(2,3,4),B(-1,-2,1),C(5,8,7)$
Direction ratio of line joining $A$ and $B$ are
$(-1-2),(-2-3),(1-4)$
$=(-3,-5,-3)$
Direction ratio of line joining $B$ and $C$ are
$(5-(-1)),(8-(-2)),(7-1)$
$=(6,10,6)$
It is clear that the direction ration of $AB$ and $BC$ are proportional, hence $AB$ is parallel to $BC$ .
But $ B$ is common to both $AB$ and $BC$
Therefore $A,B,C$ are proportional and collinear.

 

answered Jul 20, 2013 by balaji.thirumalai
 

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