The epsilon-delta definition of limit
This applet demonstrates the epsilon-delta definition of limit. Portions of the graph of f for which |f(x) - L| is *not* less than epsilon are highlighted in red. When the value of delta is "good enough" (that is, it satisfies the definition: if |x -a| is less than delta, then for such x, |f(x) - L| is less than epsilon) the relevant portion of the graph is highlighted in green. Different functions can be used by typing "f(x) = ...." into the input box.