Find the number of polygon diagonal formula! Such as the title! To explain!

Find the number of polygon diagonal formula! Such as the title! To explain!

The number of diagonals of an n-polygon is n (n-3) / 2. Because each vertex and its own and two adjacent vertices cannot be diagonals, so each vertex of an n-polygon can only be diagonals with n-3 other vertices. Because each diagonal has to connect two vertices, it needs to be divided by 2

The number of all diagonal lines in a polygon with 2n sides is 6 times of that in a polygon with n variables. Find the number of sides of the two polygons

The number of all diagonal lines in a polygon with 2n sides is 2n (2n-3) / 2 = n (2n-3), and the number of all diagonal lines in a polygon with n sides is n (n-3) / 2. According to the meaning of the problem, the following equation can be obtained: 6 × n (n-3) / 2 = n (2n-3) 3N (n-3) = n (2n-3) 3 (n-3) = 2n-33n-9 = 2n-33n-2n = 9-3n = 62n = 2 × 6 = 12

The number of diagonal lines of a polygon is equal to its number of sides. What is the number of sides of the polygon?

The number of sides of this polygon is 5. All the diagonals of the Pentagon are connected to form a five pointed star with exactly five lines