Question 156414
Use the two-point form of a straight line against two of the points and then test the other point against the rule you develop to see if the three given points are colinear.


{{{y-y[1]=((y[1]-y[2])/(x[1]-x[2]))(x-x[1])}}}


Let {{{P[1]}}} be (5,3) and {{{P[2]}}} be (4,2.2)


So {{{y-3=((3-2.2)/(5-4))(x-5)}}}


{{{y-3=0.8(x-5)}}}


{{{y-3=0.8x-4}}}


{{{y=0.8x-1}}} is your rule.  Now check the other point:


Does {{{0.6=0.8(2)-1}}}?  {{{0.6=1.6-1}}}, {{{0.6=0.6}}} -- Yep.


So your rule fits all three points and you are good to go.