Find the value of c such that the three points (5,5), (3,1) and (6,c) lie on the same line.
Note: Three points are on the same line if the slope of the line through any two points is always the same.
Slope = ( 1 - 5) / ( 3 - 5) = -4 / -2 = 2
So
(c - 1) / ( 6 - 3) = 2
(c -1) / 3 = 2
c - 1 = 3 * 2
c - 1 = 6
c = 6 + 1 = 7
