Do the points a, b, and c lie on the same line? explain your answer.

points:
a (2,4)
b (5,1)
c (-3,8)

No the given points doesn't lie on the same line. the straight line equation for the first two points is x+y=6. The third point doesn't satisfy this equation and hence the three points are not on the same line.
Note: Straight line equation for given two points:
(x2-x1)(y-y1)=(y2-y1)(x-x2)

The answer is