How many sides does a pentagon have?
A pentagon has five sides and five angles. In a regular pentagon, all sides are equal and each interior angle measures 108 degrees.
The name comes from the Greek pente, meaning five. The interior angles of any pentagon add up to 540 degrees. Drawing all the diagonals inside a regular pentagon creates a five-pointed star called a pentagram, with a smaller pentagon in its center. The golden ratio appears in many of these measurements.
Unlike squares and hexagons, regular pentagons cannot cover a flat surface without leaving gaps. Mathematicians have, however, found 15 types of irregular pentagons that can tile a plane. The last of these was discovered in 2015, and in 2017 it was proved that the list is complete.
Famous pentagons
The Pentagon, the headquarters of the US Department of Defense in Virginia, is named after its five-sided shape. It is one of the largest office buildings in the world. Pentagons also appear in nature, in flowers with five petals and in the shape of okra pods and starfish.
Did You Know?
A classic soccer ball is made of 12 black pentagons and 20 white hexagons sewn together into a shape called a truncated icosahedron.