Continuity is an important but simple concept. Basically, a continuous function is one that you could draw without having to lift your pencil. A function can be continuous throughout its entire domain, or only on a particular interval. The following are examples of functions that are not continuous:
In general a function, f(x), is continuous at some point, x = a, as long as 3 conditions are satisfied:
Intermediate Value Theorem
This theorem is a good one to know because it shows up in many proofs.
Suppose that a function, f, is continuous on an interval that includes the points a and b with a < b and that L is a number between f(a) and f(b), then there is at least one number x with a ≤ x ≤ b such that f(x) = L.
Shenk, A. (1988). Calculus and Analytic Geometry [4th Ed.]. Glenview, IL: Scott Foresman and Company.
Swokowski, E., Olinick, M., Pence, D. & Cole, J. (1994). Calculus of a Single Variable [6th Ed.]. Boston, MA: PWS.