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 .