Answer

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A = 19
s = 1.7531475747575
P = 15.778328172817
Interior Angle sum = 1260°
Diagonals = 27
1 vertex Diagonals = 6
Triangles = 7
Sides (Edges) = 9
Faces = 1
Vertices = 9

↓Steps Explained:↓

The Area of a nonagon is 19

Calculate side, perimeter

Calculate side:

A = 9/4s²cot(180°/9)

s² =	4A
	9cot(180°/9)

s² =	4 x 19
	9cot(20)

s² =	76
	9 x 2.7474774228644

s² =	76
	24.727296805779

s² = 3.073526418878

s = √3.073526418878

s = 1.7531475747575

Calculate Perimeter:

P = 9 x side

P = 9 x 1.7531475747575

P = 15.778328172817

Calculate Sum of the Interior Angles:

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

Interior Angle Sum = (9 - 2) x 180°

Interior Angle Sum = 7 x 180°

Interior Angle sum = 1260°

Calculate polygon diagonals

Diagonals =	n(n - 3)
	2

Diagonals =	9(9 - 3)
	2

Diagonals =	9(6)
	2

Diagonals =	54
	2

Diagonals = 27

Calculate 1 vertex diagonals:

1 vertex Diagonals = n - 3

1 vertex Diagonals = 9 - 3

1 vertex Diagonals = 6

Calculate triangles from one vertex:

Triangles = N - 2

Triangles = 9 - 2

Triangles = 7

Other Properties:

Sides (Edges) = 9

Faces = 1

Vertices = 9

Final Answers