In this problem the input is the coordinate of the three points in a XY plane?
P1(X1,Y1)
P2(X2,Y2)
P3(X3,Y3)
how can we find out if all the three points are on the same line or not?
for example the points (1,1) , (-1,-1) , (0,0) are on the line y=x.
Line, plane, two points, three points???
I think you should put some order in your mind (and in description also) ... :)