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A plane figure with five straight sides and five angles.
‘Similarly, nine atoms can form a pentagon bonded to a hexagon, each ring sharing two atoms with the other ring.’
‘For those who don't know, a buckyball is an extremely stable soccer-ball-shaped molecule made up of 20 hexagons and 12 pentagons.’
‘Thus, you can readily obtain a curved pentagon, heptagon, and so on.’
‘Of course, this statement has to be explained, since it is untrue if we understand distance in the usual way: the edges of these pentagons are visibly not straight and do not have the same length.’
‘The hexagons, pentagons, and triangles that make up the biomes all have their own unique specification due to the irregular nature of the site.’
‘Analysts also use a variety of symbols, such as parallelograms, pentagons, and others, to depict different types of events and activities.’
‘They are formed from 60 atoms of carbon bonded together in a combination of pentagons and hexagons to form a ball, just like a soccer ball.’
‘Although it is impossible to inscribe a regular pentagon in a square, an equilateral pentagon can be inscribed in two ways.’
‘He calculates the side of a regular pentagon in terms of the radius of the circumscribed circle.’
‘You may know about a pentagon, a hexagon, or an octagon.’
‘When I looked at what she was doing, she was trying to work out (on the napkin) how to calculate the sum of the internal angles of a pentagon.’
‘Write the number 1 through 10 in the boxes below so each side of the pentagon has a sum of 14.’
‘The balls are made with small pieces of wood 12 pentagons and 20 hexagons which fit together to form a sphere.’
‘In the second case, if the convex polygon is a pentagon incorporating all five points, then any four of these points can be connected to form a quadrilateral.’
‘This says that the most stable arrangement is a pentagon surrounded by five hexagons.’
‘Father entered the room, arms full of suitcases shaped in rectangles, pentagons, squares, and even spheres.’
‘In plan, the building is comprised of five concentric pentagons, known as rings.’
‘There are 24 ways to do it - make 12 pentagons, so that the mirror images are on each side of the pentagon.’
‘Perfect crystal structures can contain pyramids, cubes, or hexagons, but not pentagons.’
‘They are marked by a pentagon with three overlapping triangles.’
Origin
Late 16th century: via Latin from Greek pentagōnon, neuter (used as a noun) of pentagōnos ‘five-angled’.
1The pentagonal building serving as the headquarters of the US Department of Defense, near Washington DC. Part of the building was badly damaged in the terrorist attacks of 11 September 2001.
1.1The US Department of Defense.
‘the Pentagon said that ten soldiers had been killed’