$\"\"$

The series is $\"\"$ .

Consider $\"\"$ .

Hence $\"\"$ .

Substitute the corresponding values in $\"\"$ . $\"\"$

$\"\"$

If the value of $\"\"$ then $\"\"$ .

$\"\"$ .

The series is converges only at its center $\"\"$ . $\"\"$

The series is converges only at its center $\"\"$ .