A polygon is a flat 2-dimensional (2D) shape made of straight lines. The sides connect to form a closed shape. There are no gaps or curves.
(straight sides)
a Polygon
(has a curve)
a Polygon
(open, not closed)
Polygon comes from Greek. Poly- means "many" and -gon means "angle".
Example: Stop SignA stop sign is an example of a regular polygon.
It has eight equal sides and angles, making it a regular octagon.
Can you think of more polygons in real life?
Types of Polygons Regular or IrregularA regular polygon has all angles equal and all sides equal. Otherwise it is irregular
Concave or ConvexA convex polygon has no inward-pointing angles: internal angles are at most 180°.
If any internal angle is greater than 180° then the polygon is concave. (Think: concave has a "cave" in it)
Simple or ComplexA simple polygon has a single, unbroken boundary, and it doesn't cross over itself. A complex polygon has sides that intersect, making many polygon rules invalid.
More Examples(a "star polygon",
in this case a
pentagram)
Names of PolygonsYou can make names using this method:
Sides
Start with...20
Icosi...30
Triaconta...40
Tetraconta...50
Pentaconta...60
Hexaconta...70
Heptaconta...80
Octaconta...90
Enneaconta... 100 Hecto... etc..Sides
...end with+1
...henagon+2
...digon+3
...trigon+4
...tetragon+5
...pentagon+6
...hexagon+7
...heptagon+8
...octagon+9
...enneagonExample: a 62-sided polygon is a Hexacontadigon
BUT, for polygons with 13 or more sides, it is OK (and easier) to write "13-gon", "14-gon" ... "100-gon", etc.
Remembering Quadrilateral (4 Sides)
A Quad Bike has 4 wheels
The "Pentagon" in Washington DC has 5 sides
Honeycomb has Hexagons
Think Septagon is a "Seven-agon"
Octagon (8 Sides)
An Octopus has 8 tentacles
Think Nonagon is a "Nine-agon"
Decagon (10 Sides)Think Decagon has 10 sides,
just like our Decimal system has 10 digits
629, 630, 633, 634, 2125, 2126, 3255, 3256, 2127, 3257
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