Question

A polygon has 20 diagonals the number of sides are​

Answer 1

Step-by-step explanation:

diagonals of the polygon = 20

sides = 8

because n[n-3/2]=8[8-3/2]

                            =8[5/2]

                            =40/2

                            =20

answer  = 8 sides

   

Answer 2

Step-by-step explanation:

an octagon has 8(8−3)/2 = 8×5/2 = 20 diagonals. a triangle has 3(3−3)/2 = 3×0/2 = 0 diagonals