Collinear points
Definition:Three or more points that lie on the same straight line are called to be Collinear.
Three points (xi , yi , zi), where i = 1, 2, 3, are collinear if x2 - x1 : y2 - y1 : z2 - z1 = x3 - x1 : y3 - y1 : z3- z1.
X---------Y--------Z