If the function f(x) = 2x3 - 9ax2 + 12a2x + 1, where a > 0, attains its local maximum and local minimum values at p and q, respectively, such that p2 = q, then f(3) is equal to :
- 55
- 37
- 10
- 23
Answer
(2) 37
Solution
f'(x) = 6x2 - 18ax + 12a2 = 6(x - a)(x - 2a) and f''(x) = 12x - 18a.
a > 0, f''(a) = -6a < 0 and f''(2a) = 6a > 0, so there is a local maximum at p = a and a local minimum at q = 2a.
p2 = q a2 = 2a a = 2
f(x) = 2x3 - 18x2 + 48x + 1
f(3) = 54 - 162 + 144 + 1 = 37
Answer: (2)