Answer:
 g(x) is f(x) expanded horizontally by a factor of 2 
Explanation:
Given:
 f(x) = 16^x
 g(x) = 16^(x/2)
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Replacing x in a function with x/k expands the graph horizontally by a factor of k. Here, it seems we have ...
 g(x) = f(x/2)
so g(x) is a horizontal expansion of f(x) by a factor of 2.