A6. Which polygon has twice as many diagonals as sides?
(A) pentagon
(B) hexagon
(C) heptagon
(D) octagon
(E) decagon
A6. The number of diagonals in an $n$-gon is calculated by the equation $d_{n}=\frac{n \cdot(n-3)}{2}$. A heptagon has $d_{7}=$ $\frac{7 \cdot(7-3)}{2}=14$ diagonals and 7 sides, thus it has twice as many diagonals as sides.