Answers

2016-02-07T12:04:43+05:30
As the points are collinear the area of the triangle is 0. So put this coordinates in the formula of area of the triangle = 1/2 {x1(y2-y3)+x2(y3-y1)+x3(y1-y2)}
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2016-02-07T12:05:45+05:30
Area should be zero and therefore discriminant should be zero
  \left[\begin{array}{ccc}k&-k=1&-4-k\\2-2k&2k&6-2k\\\end{array}\right] =o
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