Geo2.15

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Show that the points (-5,1),(5,5),(10,7)\, are collinear.

Equation of the line joining the first two points is

y-1={\frac  {5-1}{5+5}}(x+5)\,

y-1={\frac  {2}{5}}(x+5)\,

5y-5=2x+10\,

2x-5y+15=0\,

Now if we prove that the third point lies on this equation, then the three points are collinear.

2(10)-5(7)+15=-15+15=0\,

Hence the three points are collinear.


Main Page:Geometry:Straight Lines-I