2012-02-14 12:00:43

If f (x) = x³ + ½x and g (x) = f (2x), what is g (4)?

(A) 132
(B) 136
(C) 512
(D) 516
(E) 520

The correct answer is D

Explanation: If g (x) = f (2x), that means that g (4) will equal the output created by f (2 • 4), since the output of g (x) is equivalent to the solution or result of f (2x). So, all you’re looking for here is f (8) (since 2 • 4 = 8). Plug 8 in for x in the f function: (8)³ + ½(8). This equals 512 + 4, which is 516, making choice D correct.