Ok, i am hoping we can (owing to the large amounts of questions in the homework help on stuff like this) create a nice guide for Calculus in 3D including definitions, practise questions and general examples. Firstly, i know something i really do not like is Limits. My text book gives the definition of: "Suppose l is a real number. Then the limit of f(x), as x approaches c, is equal to l if for any number e > 0 there exists a number d >0 such that |f(x) - l | < e whenever 0 < | x - c | < d" now, in terms that i can understand ( i hate the way that is all shoved into one sentence there has to be someone who can break it up so that it makes sense!) i have found this definition: I tell you how close I need to be, and you can tell me what I have to do to be that close. (from http://www.karlscalculus.org/calc2.html ) ok now. this needs to be related back. lim f(x) = L x > a This is the limit of f(x) as x approaches a. No worries there. Now what is L?