User blog:Boris Huller/need some help

Are there any article I can read to familiar with how to calculate the rate of growth? I am new here so I do not much about it yet. Several days before I post a function designed by myself, and some kind people @Alemagno12 tolerate my horrible handwriting and give me an answer. I do not mean that I don't trust him, but I am not sure whether my words can clarify my meaning or not. So I think it is better to calculate by myself. I will be very happy if anyone else can take a brief glance of the function I defined.