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## Geometry <159

### Course: Geometry <159 > Unit 1

Lesson 1: Basic 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(13 votes)
- 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.(56 votes)

- Can a rectangle be a sqaure?(26 votes)
- a square can be a rectangle but a rectangle cannot be a square(28 votes)

- What is a shape called if it has 100 sides?(25 votes)
- For short, it can be a 100-gon, but it is called zocchihedron.(14 votes)

- Can something have a different amount of sides and corners? Like 4 sides and 5 corners?(18 votes)
- accutually, a 'v' has two sides and one corner. Open shapes will have a different number of sides and corners, closed shapes will not.(11 votes)

- Are there any other differences between an oval and a circle (or is the length the only difference)?(0 votes)
- 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(19 votes)

- Why do shapes like pentagon always have the word gon(6 votes)
- 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".(3 votes)

- What's an octagon?(5 votes)
- An octagon is a shape with 8 sides.(4 votes)

- 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 at2:57and at2:06.(4 votes)
- 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!(5 votes)

- Whats the difference between a circle and a oval?(2 votes)
- An oval is slightly rounded or elongated, might be an ellipse, might be a circle too if it is the same shape as a circle. A circle is completely round, all the edges are the same distance away from the center. So an oval can be longer along one side than another.(5 votes)

- Can a shape have both curved edges and straight edges?(3 votes)
- Yes, that is certainly possible.

For example, take a sheet of paper. Now, cut it in the middle of it, in a nice bow, just to the other side of the paper.

You would have something like this: (_| (with another straight line above). It has straight edges because it was a sheet of paper, but it has curved edges where you have cut a bow.(2 votes)

## Video transcript

- [Voiceover] Oh look, it's my cousin Fal! Cousin Fal, what can I do for you? - [Voiceover] Hey Sal, what's up? - [Voiceover] Oh, well not
much, I'm just sitting here thinking about what
video I should do next. - [Voiceover] Well then
maybe you can help me. I'm starting a shape collection. - [Voiceover] Okay, so
how do you need help? - [Voiceover] Well look
at these shapes over here! I have no way to classify them! - [Voiceover] Okay, well
there's a bunch of ways that you could classify them. The first way, you could think about how many sides each of these shapes have, so that's one way to think about it, how many sides they have. - [Voiceover] How do I figure that out? - [Voiceover] Okay, well
let's look at each of these and think about how many sides they have. So this first shape right over here this is one side. We see this kind of
straight right over here, it's the straight line
between these two corners, so that's one side. Two sides, three sides, and four sides. So this shape right over
here has four sides. - [Voiceover] Okay, I think I get it. What about this shape right over here? - [Voiceover] Okay,well let's see. This one, well same idea, this one also looks like it has one, two, three, and four. Four sides. - [Voiceover] What about this one? - [Voiceover] Okay, well this one, actually this is interesting. This one actually had no corners, and it has no sides, there's no straight edges over here, this thing is all curved. So since it has no corners, it also has no sides, or at least the way that
I'm thinking about it. So I would say that this one over here has zero sides. Let me write that a
little bit neater for you. - [Voiceover] Okay yeah, I like
to write things really neat. - [Voiceover] Okay, zero sides. And it has zero corners. Actually let me write
them for all of them. This one has four sides, and we could also count the corners. We have one, that's
where the two sides meet. One, two, three, four corners. This shape over here, it also has four sides, we already counted that and it has one, two, three, four corners. So four sides and four
corners actually describes both of these shapes, this one has zero sides and zero corners-- - [Voiceover] What about the green one? - [Voiceover] Okay, well let's just see. One side, two sides, three sides, and four sides, and it also has one,
two, three, four corners. So this is also four
sides and four corners is also true of that one there. - [Voiceover] Do all shapes have four sides and four corners? - [Voiceover] No no, not at all. I mean this one right over here had zero sides and zero corners, and actually this last
shape right over here, doesn't seem to have four
sides or four corners. If we count them, we have one side, two sides, and three sides. So this one has three sides, and if we count the corners we have one corner, two corners, and three, and three corners. - [Voiceover] Oh, thanks a
bunch Uncle-- Cousin Sal. But I always get confused whether you're my cousin or my uncle. But I'll call you Cousin Sal. But I read in a shape magazine that there was other
ways that I can classify. I can classify based on whether the sides have the same size. So which of these have all the sides are the same size? - [Voiceover] Okay, well calm down. Let's look at this. So if you look at this
one, it has four sides. But we see, that this
side right over here, this green side, is clearly shorter than this purple side. So all the four sides here
are not the same length. But if we look at this
shape right over here, this side at least looks like
the same length as this side. And that looks like the
same length as this side, and that looks like the
same length as that side. So it looks over here like all four sides are the same length. And that's also true for this shape. This side looks the same
length as that side, looks the same length as that side, looks the same length as that side. That's also true for
this three-sided shape. This side looks the same
length as that side, This is the same length as that one. - [Voiceover] Oh, thank
you so much Cousin Sal! I'm ready to go classify
my shape collection. This is awesome! - [Voiceover] Well I'm
glad that I could help!