Reflection of a point $(x,y)$ in a given line $ax+by+c=0$

Friends,

The answer to the title of the post can be found here at the following link,

https://drive.google.com/file/d/0By83v5TWkGjvb2tuekNSUFo3cFE/view

Also, one can see alternative approaches to the same problem in the following link,

https://math.stackexchange.com/questions/1013230/how-to-find-coordinates-of-reflected-point

The very idea that one implements in the first link will be absolutely clear if one understands the following procedure,