A 10-sided figure is called a decagon. In geometry, a decagon is defined as a polygon consisting of 10 connecting line segments that connect at 10 vertices. A regular decagon has sides with equal lengths and equal angle measurements.
The interior angles in a regular decagon each equal 144 degrees in size. The area of a regular decagon is found by multiplying two and a half times the distance between any two parallel sides, then multiplying that number by the length of one side. The perimeter of a regular decagon is found by multiplying 10 times the length of one side. A three-dimensional figure with 10 faces is called a decahedron.