Find a relation between x and y if the points (x, y), (1, 2) and (7, 0) are collinear
If the given points are collinear, then the area of triangle formed by these points will be 0
Area of the triangle = 
[x1 (y2 – y3) + x2 (y3 – y1) + x3 (y1 – y2)
= 
[x (2 – 0) + 1 (0 – y) + 7 (y – 2)
0 = 
(2x – y + 7y – 14)
2x + 6y – 14 = 0
x + 3y – 7 = 0
This is the required relation between x and y
2