How to make a random number generator based off a number

I need a random number generator that is based off of an equation. I want to take to numbers and subtract and that would be x and then that would be the equation it would be based off of.

 

check here for generating randoms.
if you want something else explain better.

http://www.cs.geneseo.edu/~baldwin/reference/random.html

 

Disregard this thread and look at my other one.