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## Geometry (all content)

### Unit 3: Lesson 6

Geometric solids (3D shapes)# Recognizing common 3D shapes

Sal identifies the following 3D shapes: square pyramid, rectangular prism, triangular prism, cylinder, and cone.

## Want to join the conversation?

- how do i find surface area(15 votes)
- You find the area of each side of the object and then add them all together.(13 votes)

- Would a shape with an octagon for a base and triangles for sides meeting at a point be called an octagonal pyramid?(6 votes)
- Yes,an octagonal pyramid is a pyramid with a base that's a polygon with eight sides, or an octagon, and triangular faces, or sides, that meet at a point directly above the bottom.(2 votes)

- At1:50, Sal says "This has sides that are triangles", doesn't he mean faces?(3 votes)
- I think he means bases.(3 votes)

- I don't know what a vertice is(3 votes)
- 頂点は、3つのエッジの交点です。 It is the intersection of three edges.(2 votes)

- what the differences between vertices and edges?(3 votes)
- A vertex is where two or more edges meet, so a vertex is a point and a edge is a line segment.(3 votes)

- Would a shape with an octagon for a base and triangles for sides meeting at a point be called an octagonal pyramid?(3 votes)
- Yes a pyramid has a single base and a vertex where all lateral edges meet. You always name a pyramid (and a prism) by the shape of the base.(2 votes)

- Which figure does not belong with the other three and explain if you have a triangle, cube, sphere, and cylinder(2 votes)
- It is the triangle because it isn't a 3 dimensional shape. If it is 3 dimensional, then it's the sphere because it has no edges.(4 votes)

- What kind of polygon have 100 sides ?(2 votes)
- Think of a century as 100 years, so it would be a centagon. This is like a decagon is like a decade (10 years).(4 votes)

- A sphere is a circle right?(2 votes)
- It may seem that way, but technically, a sphere is a 3-D shape (has width, height, and depth) and a circle is 2-D (width and height) A circle is missing the depth needed to become a 3-D shape. Also, you find volume for spheres and area for circles. This then changes the formulas.

Circle: A = pi*r^2

Sphere: V = 4/3*pi*r^3

Good luck in your journey through geometry!(5 votes)

- what is a vertice?(2 votes)
- A vertex (vertices is the plural of vertex) is a point where the sides of a shape intersect. So basically any corner on a shape is a vertex.(9 votes)

## Video transcript

- [Teacher] I have five
three-dimensional shapes over here. I also have five names for them. What I want you to do is pause this video and think about which of these
shapes is a square pyramid. Which of these is a rectangular prism? Which one is a triangular prism? Which one is a sphere and
which one is a cylinder? Let's just work through this together. Really, this is just something to know, because some people in various subjects will sometimes throw out these words. First, let's think about which
one is the square pyramid. This shape here on the right
clearly looks like a pyramid, and the thing that makes
it a square pyramid is the idea that its base is a square. Let me see if I can shade this in. So the base of this right over here is a square. That's where the square
pyramid comes from. If it's a triangular pyramid, then the base would only have three sides, but this is a square pyramid. So let me... Move this over there. So that is a square pyramid. Alright, let's do the next one. Which one is a rectangular prism? A prism you can view as a
three-dimensional object, and since it's saying a rectangular prism, well, the best one here
that is rectangular, notice, this shape right
here is rectangular on every side, and it's three dimensions. It is a prism, and so this
is the rectangular prism. So let's move that over. So that is our rectangular prism. Now, triangular prism. So this one is interesting. If you look at this shape right over here, it has sides that are triangles. You see this up here is a triangle and you see this down here is a triangle, although they're connected
by these rectangular sides. This is actually what's
called a triangular prism. In a square pyramid, the
faces which are triangles all meet at a point. In a triangular prism, you
have two opposite-facing sides that are triangles. You'll see all of these
in different orientations. Sometimes it'll be resting like this, sometimes it'll be on it's side, but this is a triangular prism. Let me... So that is a triangular prism. And so we have two left. You might be able to figure these out. Which one is a sphere? When I think sphere, I think of a globe. This choice right over
here is clearly a sphere. Let me move that over. Let me move it over, okay,
so that one is a sphere. Then last but not least, this
thing that looks like a can is a cylinder. So let me move that over. So that is a cylinder. And we're all done. So these are just useful
names to know for shapes. Cylinder is... You have these two faces that are circular and then they are opposite each other. It's kind of like a triangular prism, but instead of having these hard edges because you have a
triangle, you have a base that is a circle and a
top that is a circle.