Lesson video

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Hi, everybody.

I'm Ms. Miles.

Before we get started, did you know a fact? Today's fact is, did you know that opposite sides of a dice always add up to seven? You could get a dice and check that.

Okay, moving on.

So today, we're going to complete lesson three in our unit on 2D and 3D shape.

You need to have completed lessons one and two before you complete this one, so if you haven't done that, please go and do that first.

For today's lesson, you will need a pencil, a piece of paper, and a clear workspace.

Let's get started.

So in today's lesson, we are going to be identifying regular and irregular polygons.

Let's go, on screen, you will say a variety of shapes.

The question is, which of these shapes are polygons.

Now, a polygon is a 2D shape that has three or more straight sides.

If it doesn't fit that criteria, it is not a polygon.

I'll say that again, a polygon is a 2D shape with three or more straight sides.

So looking at the images on screen, pause your video and identify which shapes are polygons and which ones are not, off you go.

Okay, so you may have noticed that there are quite a few shapes on there that are not polygons.

I can see a circle, and an oval, and the semicircle on there, and they would not be polygons because they do not have three or more straight sides.

In fact, they all have curves, so they are not polygons.

However, I can see a hexagon, I can see different varieties of triangle.

I can also see a rectangle, and I know that they are all polygons because they have straight side, and they have three or more straight sides.

So what I'd like you to do now for me is have a go at filling this frame model.

So in the middle, it says polygon.

And around the side, there are different boxes for you to fill in.

You need to write a definition of the word polygon, facts about polygons, examples of different polygons and non-examples.

That means shapes that would not be polygons.

So I'd like you to draw that, fill it in with as much information as you can.

And then I'll share mine and we will compare, pause your video there.

So I'm going to show you my frame model now.

So I've drawn one out similar, same as you would have done.

And here is mine, I'll push it forward to the screen, so that you can see.

So for my definition, I have written, a closed plain figure with three or more straight line segments.

Basically, what I mean there is a closed figure or closed 2D shape with three or more sides.

When I've put a closed plain figure, what that means is that all the sides must connect.

If there are any gaps or it is open at any point, it is not a polygon, Facts about polygons, I've written that shapes must be closed.

They must have three or more straight sides, and they are 2D or two dimensional.

Some examples of polygons here, I've put rectangle, square, triangle, trapezium, and a hexagon.

Now, obviously, that's not all of the different examples, you might have put different ones today.

And here are some of my non-examples here, can see, I popped a circle on there, a semi circle, 3D shapes, 3D shapes are not polygons because polygons must be 2D.

And then 2D shapes that are not closed.

So any 2D shapes that are open at any point, they are also non-examples of polygons.

You could have also put on there an oval.

Okay, how did you get on with that? If you need to add any extra information, please do that now.

So moving on, on screen, there are three different types of triangle.

The question is how many different ways can you draw a triangle? Now, there are three different ones on screen.

I can see there's a right angle triangle there.

That is also scaling because it's got three different size, that's the blue one.

The purple one has got three sides that are all the same length, that's an equilateral triangle.

And I've also got an isosceles triangle, which is my white one because it has two sides that are equal length and one side that is not.

So bearing that in mind, I would like you to have a go at this next question.

How many different ways can you draw a hexagon? So what do you know about hexagon already? I know quick tip that a hexagon has got six sides.

Pause the video there.

How many different hexagons can you draw? Okay, onscreen now, here are some different varieties of hexagon.

You can check them if you want to, they have all got six sides.

They're all polygons because they are 2D.

They have three or more straight sides and they are all closed shapes.

So these are different varieties of hexagons, all six sides, all polygons.

You might've got some different ones.

These aren't the only answers, you might have drawn something slightly different and that's absolutely fine.

So let's have a look at this one now.

So here are some different shapes on the screen that I'd like you to have a go at drawing.

There's a Pentagon, a heptagon, an octagon, and a decagon.

I would like you to pause the video and draw as many different varieties of those shapes as you can, make sure that they have got the correct number of sides, pause the video there.

Okay, so here are some examples that you could have come up with.

A pentagon is a five-sided polygon, a heptagon is a seven-sided polygon, an octagon is an eight-sided polygon, and a decagon is 10-sided polygon.

Again, you might have joined different ones, but here are some examples of what you could have drawn.

So now, we're going to have a think about regular and irregular shapes.

Regular shapes are shapes that have all sides of the same length and all angles of the same size.

And irregular shapes are shapes that side lengths that are different and angle sizes that are different.

So let's have a look at those triangles, again, from earlier.

These are the three triangles that we looked at earlier, which one of those triangles would be a regular triangle.

So I know that a regular shape is a shape that has got all sides that are the same length and all angles that are the same size, so if I look at my blue triangle, I can see that it's got a right angle.

I can also see that it's got two acute angles and all three sides are different lengths.

So that one can not be a regular triangle.

Let's have a look at the purple one.

I can see that it has got three sides that are all the same length.

And I can see that it's got three angles that are all acute and all the same size.

Again, let's have a look at the white one.

No, I know that the white one has got two sides that are the same, but one is different.

So the regular triangle would be the purple one, which is an equilateral triangle, three sides of all the same length, three angles of all the same size.

So here's an image to show that's a little bit further.

Here's an equilateral triangle, three sides the same length, three angles the same size.

Now, looking at these images on screen, which of these quadrilaterals is a regular quadrilateral and how do you know? Pause the video there and have a look at the shapes and work out which one is regular.

And you must think about why that is, pause the video there.

So of the three shapes on the screen, the first shape is a rectangle.

I know that a rectangle has two opposite sides of the same length, so the two sides opposite end are both the same, those shorter sides.

And the two sides going this way are longer sides and they are the same, but because all the side lengths aren't the same, that one can not be regular.

Okay, now, looking at the parallelogram on the right hand side, again, I can see that it's got two sides that are the same length and the opposite sides are the same length.

So that one is not a regular quadrilateral there because he doesn't have four sides all the same length.

However, my square in the middle is a regular quadrilateral because it has got four right angles and four sides are the same length.

Did you get the same answers there? Okay, it's time to apply all of that learning to your independent task.

So independent task number one, here, there are two different shapes on screen, and they have got angles and side lengths labelled on.

I would like you to name each of the shapes, identify if they are regular or irregular.

Explain how you know that.

Find the sum of the interior angles.

That means I would like you to add some of them up together to find out what the overall total would be.

And I'd like you to find the perimeter.

The perimeter is the overall distance of the outside of the shape.

So you will need to look at the different lengths of the sides and total them up together.

Pause the video there and have a go at that one.

Independent task number two, there are four different shapes on your screen, I would like you to name those shapes.

I would like you to decide if they are regular or irregular, and explain how you know.

To name the shapes, what I would do is I would count how many sides each shape has got all together, and that will tell me the type of shape that it is, and then I will consider whether it's regular or irregular.

Pause the video there and have a go at that one.

Okay, let's have a look through their answers now then.

So here are your answers for task number one.

Shape number one is a pentagon, it is regular.

I can see that because the sides are the same length.

All the angles and sides are equal, which again is a reason for why is a regular shape.

And the interior angles add up to 540 degrees.

And the overall perimeter is 50 centimetres.

My second shape is a hexagon because it has six sides.

However, this time, it is irregular because all the angles and sides are not of equal size or length.

The internal angles add up to 720 degrees.

and the overall perimeter is 66 centimetres.

Have a look at how you got on and make any corrections, if you need to.

And here are the answers to task number 10, our first shape is a heptagon and it is irregular because there are different length sides and different degrees of turn inside the shape.

My second shape is a heptagon, again, but this time is in regular heck to go because the sides are the same length and the internal angles are also the same size.

My first shape is an octagon, an eight-sided shape.

This one is regular with same lengths sides and the same size of internal angles.

And our last shape, it's also an octagon, but this time it is an irregular octagon because the sides are different length, and our internal angles are also of different size.

Again, check your answers for me and compare them with the ones on screen, and make any changes if you need to.

Okay, well done for completing today's lesson, please, don't forget to complete the end of lesson quiz and I'll see you again very soon.