The Expression May Be Factored as Shown $2 ^ { 3 x / 2 } + 2 ^ { - x / 2 } = \sqrt { 2 ^ { - x } }$

Short Answer

The expression may be factored as shown. Find the missing factor. $2 ^ { 3 x / 2 } + 2 ^ { - x / 2 } = \sqrt { 2 ^ { - x } }$ ( )Enter your answer as $2^ a$ + b.