1. polygon

How many diagonals does a regular seven-sided polygon contain?

2. Hello, sri340!

How many diagonals does a regular seven-sided polygon contain?

Take the 7 vertices, 2 at a time: . $_7C_2 \:=\:\frac{7!}{2!\,5!}$

3. Originally Posted by Soroban
Hello, sri340!Take the 7 vertices, 2 at a time: . $_7C_2 \:=\:\frac{7!}{2!\,5!}$
... But if you take a "diagonal" to mean a line connecting two non-adjacent vertices then the answer will be less (14, in fact).