calculating linear equation of a line from line segment
<p>Ideally, each of our lines will be in the form Ax+By=C, where A, B and C are the numbers which define the line. However, we are rarely given lines in this format, but we can easily generate such an equation from two points. Say we are given two different points, (x1, y1) and (x2, y2), and want to find A, B and C for the equation above. 
    We can do so by setting
    A = y2-y1
    B = x1-x2
    C = A<em>x1+B</em>y1</p>

<pre><code>The above facts is described in the link https://www.topcoder.com/community/data-science/data-science-tutorials/geometry-concepts-line-intersection-and-its-applications/

But i am unable to understand the concept of the below 

A = y2-y1
B = x1-x2
C = A*x1+B*y1

solution ( the value of A,B and C). 
</code></pre>