Carcass wrote:
How many diagonals does a regular 11-sided polygon contain?
A. 35
B. 38
C. 40
D. 44
E. 55
A nice/fast approach that doesn't involve any counting techniques is to recognize that, for each of the 11 points (vertices), there are 8 possible points that we can connect to to create a diagonal.
ASIDE: there are 8 possible points because we cannot create a diagonal by connecting 2 adjacent points.
So, there are 8 possible diagonals for each of the 11 points
These means that there are 88 possible diagonals in total (8x11=88).
However, we need to recognize that this method counts each diagonal twice. For example, it counts the diagonal AB and the diagonal BA as 2 separate diagonals.
So, to account for this duplication, we'll divide 88 by 2 to get 44
Answer: D
Cheers,
Brent