(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) .