Determine if the points (1, 5), (2, 3) and (– 2, – 11) are collinear
Assume points (1, 5), (2, 3), and ( - 2, - 11) representing the vertices A, B, and C of the given triangle respectively.
Let A (1, 5), B (2, 3) and C (-2, -11)
Now,
AB = [(1 – 2)2 + (5 – 3)2]1/2
= 
BC = [(2 + 2)2 + (3 + 11)2]1/2
= 
CA = [(1+ 2)2 + (5+ 11)2]1/2
= 
Since, AB + BC ≠ CA
Therefore, given points are not collinear
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