If you haven't learned differntiation rules then we will go with the quotient difference...ok the slope of a curve is given by ..so to get the devative of before you know differentiation rules is to go through this thus the derivative of is ...so the slope at the point x is ...so the slope of the curve of at x=2 is ...so the slope of the tangent line at the point x=2 has the same slope as the curve so its slope is 4
the limit stuff...hmm...thats something you just have to learn...here I think this will really help you its a great site..good luck! if you have any more questions just ask
Visual Calculus