The line equation passing through A (a, b) and B (c, d) is equal to =
(x - a)(b - d) - (y - b)(a - c) = 0.
For example: line equation passing through the points (1, 1)and (0, 0) is =
(x - 1)(1 - 0) - (y - 1)(1 - 0) = 0
x - 1 - y + 1 = 0
x + Y = 0.