If point (a, 0), (0, b) and (1, 1) are collinear, then  is equal to

Concept:

If three points (x1, y1), (x2, y2) and (x3, y3) are collinear then the area of the triangle determined by the three points is zero.

or

If three or more points are collinear then the slope of any two pairs of points is same.

For example, let three points A, B and C are collinear then

slope of AB = slope of BC = slope of AC

Slope of the line if two points  are given by: 

Calculation:

Given: the points (a, 0), (0, b) and (1, 1)  are collinear

ab - a - b = 0

a + b = ab