$\"\"$

The terms of the sequence are $\"\"$ , $\"\"$ and $\"\"$ .

Find the sum of first $\"\"$ terms.

Formula of $\"\"$ partial sum of geometric series: $\"\"$ .

Substitute $\"\"$ , $\"\"$ and $\"\"$ in the formula.

$\"\"$

$\"\"$ .

$\"\"$ partial sum of geometric series is $\"\"$ .

$\"\"$

$\"\"$ partial sum of geometric series is $\"\"$ .