The number of diagonals of a polygon of n sides is given by the formula f=n(n-3)/2. If a polygon has twice as many diagonals as sides, how many sides does it have? Choose the correct answer:
A) 3
B) 5
C) 6
D) 7
E) 8

Rationale: "f = n ( n - 3 ) f = 2 * n 2 n = n ( n - 3 ) = > 2 = n - 3 = > n = 5 answer b"
Answer: B