I really need some Vector help!!?

Hey there, I've been doing vectors lately and even though I understand the topic to some degree, this question has me stumped completely. P.S its not homework, I'm just revising what I did in class today.

Points A and B have coordinates (4,1) and (2,-5), respectively. Find an equation for the line which passes through the point A, and which is perpendicular to the line AB.


Just a side note, I have the answer, but I want to know how to get there and if you would PLEASE give me a step by step explanation so that I can fully understand it.


Thanks in advance :)