A decagon is a polygon with 10 sides and 10 vertices.
A regular decagon is a polygon with 10 equal sides and angles.
Angles of the Decagon
The sum of interior angles of a decagon = (10 − 2) · 180° = 1,440°
The value of an interior angle of a regular decagon is: 1,440º : 10 = 144º
The central angle of a regular decagon measures: 360º : 10 = 36º
Diagonals of the Decagon
The number of diagonals in a regular decagon = 10 · (10 − 3) : 2 = 35
Perimeter of a Regular Decagon
Perimeter = 10 · l
Area of a Regular Decagon