# Formal Limit Definition

- Author:
- Dr. Doug Davis, 3D

This is an illustration of the formal concept of a limit. One formal definition for a limit is:
Let be defined on an open interval about , except possibly at itself. We say that the limit of as approaches is the number , and write
,
if, for every number , there exist a corresponding number such the for all ,
.
If setting any goal value you can make small enough so that the above inequality holds the limit exist. There are two indications that is small enough. The brown box shows . The blue dash dot line show the minimum and maximum values of within the bounds. If both blue dash-dot lines cross the box the statement is true for the given . Also, the values are shown with a nice blue equation. The red equation with yellow background indicates that is not small enough.

For each function explore placing at different values and decreasing with the close button. Try placing on boundary circles. Note: can snap to grid values if the cursor is on the point.

- For the first two functions ( floor and ceil ) does the limit exist at any integer value?
- For all of the functions is there anywhere where the limit does not exist?
- When is the
point is not included in the Ymax and Ymin values?