On the test I had today I was asked to find the derivative of x^3+3*cos(x) using the definition of a derivative. The (f(x+h)-f(x))/h type.
So i set my function and then used the definition and then tried to simplify. Unfortunately the bottom h is still there so when I try to evaluate the function when h=0 it returns an obvious problem. It can't divide by zero. Usually when I do this the h on the bottom will be canceled out, but it wouldn't do it for this one. Does anyone know how to fix it? I have attached the file so you can see where I am stuck.