Derivatives functions

Now I'm studying derivatives functions in maths. I understand them well but, as usual, there are always some problems. For example, I have explained all of them in my notebook, but I won't be carrying it to every place I'm going to to review them, because it's cumbersome. So I thought that it would be the best to have an app about it on my phone, and I've called my cousin, who is studying Computer Engineering, to try to make this app, because he told me once that they had studied that the last course, and he has said to me that he is also studying it on this course.
He has recently told me that he will think about it these days and that he will maybe accept my idea and he will try to do it.
Now I'm looking forward to help him in this app.