The function

has a finite limit,

, as

. This means that for any

, there is an interval of width

around

(perhaps with

and

very small), such that

whenever

is in that interval. Move the point directly and adjust

using the slider. This Demonstration computes the largest

and

for a given

so that

lies between

and

. The values for

and

may be found automatically or manually by dragging. The function shown is

.