We can use any one of the following methods to prove the given three points are collinear.
.Let the points are A,B,C
1.If slope of AB=slope of BC the points are collinear
2.Using distance formula if AB+BC=AC or sum of the length any two segments is equal to the length of the third one , the points are collinear
3.Using area of a triangle formula if the area formed by these points=o they are
4. Using two points formula find the equation of a line using any two points
Substitute the third point in this equation. If it satisfies they are collinear
In all the methods using slope formula is simple