posted by cole .
What polygon has 20 diagonals?I don't know how to figur this out.
A rectangle (4 sides) has 2 diagonals.
A hexagon (6 sides) has 3 diagonals.
An octagon (8 sides) has 4 diagonals.
A _____ (20 sides) has 20 diagonals.
The no. Of diagonals in a polygon is nC2-n .So polygon with 8 sides shall have 20 diagonals