(a)

The condition is:

if  then .

 definition of limit :

,

if for every number of , there exists a  such that  whenever .

Compare the condition, if  then  with  definition of limit.

Here ,  and .

Consider .

Observe the relation between two absolute values  and .

Here .

Therefore .

when  then .

(b)

The condition is :

if  then .

Here .

When  then .

(a) .

(b) .