The inner circumference of the ring is
.
(a)
\The circumference is
.

Inner radius of the ring is
.
(b)
\The circumference vary from
and
.
The circumference is
.
If Circumference is 

Inner radius of the ring is 
If Circumference is 

Inner radius of the ring is
.
(c)
\At
the circumference of the ring is
.
.
Prove the limit
using
definition.
For each
,there exists a
such that
whenever
.
Consider

Consider 



Observe the relationship between two absolute values
and
.
.
Therefore
.
then
.
(a) Inner radius of the ring is
.
(b) Inner radius of the ring is
when circumference is
.
Inner radius of the ring is
when circumference is
.
(c)
and
.