Question

Jika f(3)=1 dan f(3n)=n+f(3n-3) dimana n adalah bilangan bulat yang lebih besar dari 1, berapakah nilai dari f(21)?


A 7
B 18
C 22
D 25
E 28

Answer 1

F(3) = 1
f(3n) = n + f(3n - 3)
n = 2 ⇒ f(6) = 2 + f(3) = 2 + 1 = 3
n = 3 ⇒ f(9) = 3 + f(3) = 3 + 3 = 6
n = 4 ⇒ f(12) = 4 + f(9) = 4 + 6 = 10
n = 5 ⇒ f(15) = 5 + f(12) = 5 + 10 = 15
n = 6 ⇒ f(18) = 6 + f(15) = 6 + 15 = 21
n = 7 ⇒ f(21) = 7 + f(18) = 7 + 21 = 28
Jawaban: E