I am using D to get derivatives of a function. However, R does not simplify the expression when returning the derivative. I need to figure out if a function has a derivative tha
As far as I know, R will not simplify the result of D(). It sounds as though you want a proper computer algebra system, and R is definitely not a full CAS. Mathematica and Maple are the most well-known, but there are also a number of open-source alternatives (as discussed on this SO post).
R can do numerical integration - for this kind of question it is worth searching in the R help pages first (i.e. help.search('integrate')). You can use integrate() in the stats package. There is also area() in the MASS package, but that is much simpler (i.e. for demonstration purposes).