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Lesson 4: Shapes

# Cousin Fal's shape collection

Sal classifies shapes based on their number of sides, number of corners, and side-lengths. Created by Sal Khan.

## Want to join the conversation?

• What are 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 sided shapes called. Also Thank you
• 3 sided shapes are called triangles,
4 sided shapes are called quadrilaterals,
5 sided shapes are called pentagons,
6 sided shapes are called hexagons,
7 sided shapes are called heptagons,
8 sided shapes are called octagons,
9 sided shapes are called nonagons,
10 sided shapes are called decagons,
11 sided shapes are called hendecagon,
12 sided shapes are called dodecagon.
• Can a rectangle be a sqaure?
• a square can be a rectangle but a rectangle cannot be a square
• What is a shape called if it has 100 sides?
• For short, it can be a 100-gon, but it is called zocchihedron.
• Can something have a different amount of sides and corners? Like 4 sides and 5 corners?
• accutually, a 'v' has two sides and one corner. Open shapes will have a different number of sides and corners, closed shapes will not.
• Are there any other differences between an oval and a circle (or is the length the only difference)?
• An oval is a circle that is elongated in some direction. A circle could be elongated by no value at all so this holds.
All circles are ovals
Not all Ovals are circles
• What's an octagon?
• An octagon is a shape with 8 sides.
• Why do shapes like pentagon always have the word gon
• Copy pasted from Wikipedia (https://en.wikipedia.org/wiki/Polygon):

Etymology:
The word "polygon" derives from the Greek adjective πολύς (polús) "much", "many" and γωνία (gōnía) "corner" or "angle". It has been suggested that γόνυ (gónu) "knee" may be the origin of “gon”.

So according to this, "gon" is the Greek word for corner or angle (which may have come from the word knee). So a "hexagon" is the word for 6 (hex) and angle (gon) so "a six angled shape".
• I've always thought corners meant where two lines meet at a 90 degree angle, but is it really just where two lines meet together? Mainly I'm asking about at and at .
• In shapes, a corner is any place at which two lines meet. In real life, you most often encounter corners that are parts of rooms, or tables, and those should be 90 degrees. Hope this helps!