### Video Transcript

Polygons and Nonpolygons

In this video, we will learn how to
identify a polygon among two-dimensional shapes.

Here are some two-dimensional
shapes or 2D shapes. How do we know if a 2D shape is a
polygon? Polygons have straight sides. The heart shape isn’t a polygon
because some of its sides are curved. The circle isn’t a polygon either
because it has one curved edge. And the oval isn’t a polygon
either. All of these 2D shapes have
straight sides. All of these shapes are
polygons.

Polygons are also closed
shapes. That means that all of the sides
are connected. This is a closed shape. All of the sides are connected. If we start at this point here and
join all of the sides, eventually, we come back to the point where we started. So all of these 2D shapes are
polygons. They’re all closed 2D shapes with
straight sides.

Is this shape a polygon? It’s a 2D shape. It’s a closed shape. And it has straight sides. So this shape is a polygon. Is this shape a polygon? This shape has a curved edge. Polygons have straight sides. So this shape is not a polygon. Is this figure a polygon? This figure is open. We know that polygons are closed
shapes, so we know that this figure is not a polygon either. We’ve learned that polygons are
closed 2D shapes with straight sides. Let’s practice identifying polygons
with some questions.

Scarlett has sorted these shapes
into polygons and not polygons. Fill in the blank. All polygons are closed and
what. Have more than four edges or sides,
have curves, or have straight edges or sides.

We know that Scarlett has sorted
her shapes into two groups, polygons and not polygons. We’re told that all polygons are
closed shapes. We have to pick another statement,
which is true. Do all polygons have more than four
edges, curves, or straight sides? Let’s check the polygons. Do all of these polygons have more
than four edges or sides? No, they don’t. There’s a triangle. We know that triangles have three
edges or three sides, so we know the first statement is false.

Do all polygons have curves? None of the polygons have
curves. Some of the shapes in the group of
not polygons have curves, but none of the polygons have curves. We know that this statement is also
false. Do all polygons have straight edges
or straight sides? Yes, they do. All of the shapes which Scarlett
has sorted into the polygons group have straight sides. We looked closely at the shapes in
Scarlett’s groups, the polygons and not polygons. All polygons are closed and have
straight edges or straight sides.

Which of these is a polygon?

We’ve learned now that polygons are
closed shapes which have straight sides. This is a closed shape and it has
straight sides. So this is a polygon. This figure is open. It’s not a polygon. This is a curved shape. So it’s not a polygon either. All polygons are closed and have
straight edges. This is the shape which is a
polygon.

Is the given shape a polygon?

We know that polygons are closed
shapes; the sides are all connected. If we started drawing at the pink
dot and drew all the way around the shape, we would come back to the start
point. This shape is a closed shape. We also know that polygons have
straight sides, and all of the sides of this shape are straight. The given shape is a polygon. So the answer to the question “is
the given shape a polygon?” is yes. We know it’s a polygon because it’s
a 2D shape. It’s a closed shape. And it has straight sides.

True or false? To draw a polygon, you must draw at
least three line segments.

Let’s draw a shape with three line
segments. One, two, three. We drew a triangle. This triangle is a polygon. It has three line segments. All of its lines are straight. And it’s a closed shape. Is it possible to draw a polygon
which has less than three line segments?

This figure is made from two line
segments. Is it a polygon? No, it’s an open shape. We know that polygons are closed
shapes. Here’s another figure made from two
line segments. This is also an open figure. So to draw a polygon, we need at
least three sides or three line segments. The given statement is true. To draw a polygon, you must draw at
least three line segments.

True or false? A polygon has the same number of
sides as vertices.

This shape is a polygon. Does it have the same number of
sides as vertices? It has six sides and six
vertices. Let’s try a different polygon. This polygon has four sides and
four vertices. We drew two polygons. Both had the same number of sides
as vertices. The statement is true. A polygon has the same number of
sides as vertices.

I want to join two vertices in this
shape with a straight line so I can create two new polygons which have the same
number of sides. Which vertices could I join? 𝐵 and 𝐹, 𝐴 and 𝐸, 𝐵 and 𝐸, or
𝐴 and 𝐶.

In this question, we have to join
two vertices from the given shape with a straight line to create two new polygons
which both have the same number of sides. If we join the vertices 𝐵 and 𝐹,
we get two new polygons. But do they both have the same
number of sides? One of our polygons has three
sides. The other has five sides. So we know it’s not 𝐵 and 𝐹.

If we join the two vertices 𝐴 and
𝐸, we get two new polygons. And again, one of our polygons is a
triangle with three sides, and the other shape has five sides. One, two, three, four, five. What happens if we join the
vertices 𝐵 and 𝐸? We’ve made two new polygons, and it
looks like they both have the same number of sides. One, two, three, four. And our second new polygon also has
one, two, three, four sides.

If we join the two vertices 𝐵 and
𝐸 in this shape, we can create two new polygons which have the same number of
sides. Both have four sides. We joined vertices 𝐵 and 𝐸.

What have we learned in this
video? We’ve learned how to identify
polygons. And we’ve learned that polygons are
closed 2D shapes with straight sides.