$\"\"$

\

The expression is $\"\"$ .

\

$\"\"$ (Expand)

\

$\"\"$ $\"\"$

\

(Apply sum of infinite geometric series formula: $\"\"$ )

\

$\"\"$ (Substitute 2 for $\"\"$ , $\"\"$ for r)

\

$\"\"$ $\"\"$

\

The sum is 6.