Answer

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P = 20
s = 2.5
A = 30.177669529664
Interior Angle sum = 1080°
Diagonals = 20
1 vertex Diagonals = 5
Triangles = 6
Sides (Edges) = 8
Faces = 1
Vertices = 8

↓Steps Explained:↓

The Perimeter of an octagon is 20

Calculate side, area

Calculate side:

s =	P
	8

s =	20
	8

s = 2.5

Calculate Area:

A = 2(1+√2)side²

A = 2(2.4142135623731)2.5²

A = 4.8284271247462(6.25)

A = 30.177669529664

Calculate Sum of the Interior Angles:

Interior Angle Sum = (sides - 2) x 180°

Interior Angle Sum = (8 - 2) x 180°

Interior Angle Sum = 6 x 180°

Interior Angle sum = 1080°

Calculate polygon diagonals

Diagonals =	n(n - 3)
	2

Diagonals =	8(8 - 3)
	2

Diagonals =	8(5)
	2

Diagonals =	40
	2

Diagonals = 20

Calculate 1 vertex diagonals:

1 vertex Diagonals = n - 3

1 vertex Diagonals = 8 - 3

1 vertex Diagonals = 5

Calculate triangles from one vertex:

Triangles = N - 2

Triangles = 8 - 2

Triangles = 6

Other Properties:

Sides (Edges) = 8

Faces = 1

Vertices = 8

Final Answers