Three points are collinear if the area of the triangle formed by them is

1. Collinear points lie on a single straight line. 2. Then they cannot form a triangle, so the enclosed area is **zero**. 3. Setting the area formula equal to 0 is the test for collinearity. _Source: Karnataka SSLC (KSEEB) Class 10 Mathematics, Ch7 'Coordinate Geometry', §7.4_