i) If three or more points lie on the same line, then the points are called collinear points.

ii) The points $A(x_1,y_1),B(x_2,y_2)\text{ and }C(x_3,y_3)$ are said to be collinear, if

a)      $|AB\pm AC|=BC$

b)      $\text{area\hspace{0.17em}of\hspace{0.17em}}\Delta ABC=0$

c)      $\frac{y_1-y_2}{x_1-x_2}=\frac{y_1-y_3}{x_1-x_3}$