Lesson video

Hi everyone, I'm Miss Mitchell.

Today in math, we're going to be recognising lines of symmetry within 2-D shapes.

So today's lesson, we will be learning about lines of symmetry.

You will then complete a talk task, an independent task, and then a quiz.

For today's lesson, you will need a pencil, some paper, and also a pair of scissors.

Please make sure you ask your parent or carer before taking these and make sure you were supervised when using them.

What's a symmetry? Symmetry is when something is identical on both sides.

Now, what does identical mean? Identical means exactly the same.

So for example, identical twins.

Identical twins look exactly the same.

So symmetrical means when it is the same, identical.

A shape or pattern has symmetry if a mirror line can be drawn on it to show that both sides are exactly the same.

So for example, here in this picture, without the line we know that down the middle, if we drew a line, that both sides would be exactly the same.

They are identical.

This means that this image is symmetrical because on both sides of the line of symmetry, which is this line down here, it looks identical.

Is there a line of symmetry? How could we check? Now, we know that this smiley face does have a line of symmetry, because if we had a mirror or wager line down here, we know that on each side, it is identical.

They look exactly the same.

The eye is in the same place.

The smile is the same.

Everything has to be the same about it.

I would like you to complete the talk task.

So what you need to get is a piece of paper.

You need to fold it in half, and then I would like you to cut a shape but without cutting where the fold line is.

So if this is the piece of paper and you folded it in half, you don't cut along this line here.

You're then going to open the shape so that you can see the line of symmetry.

And when you open it up, both sides will look exactly the same, because they are identical.

Okay, so for the talk task, you need your piece of paper.

What you're going to do, you're going to fold it in half.

Nice and straight.

And then this is where the fold is here.

You are not going to be cutting this bit.

You're going to get your scissors, asking your parents and carers permission, please.

And then you're going to maybe cut.

Not where the fold is.

I'm going to open it up and look it is identical on both sides.

This is exactly the same as this side, which means this down here is the line of symmetry, because this side is identical to the other side.

Can you please now have a go with your piece of paper? What shape is this? It has four vertices and four sides, all the same length.

Therefore, it is a square.

Now, how they think? Do you think this shape has a line of symmetry, maybe more than one line of symmetry? And where do you think the line of symmetry is? Now this shape, this square, has four lines of symmetry.

One, two, and then diagonally three and four.

If you had a piece of paper that was a square, so all the sides were the same length, you could fold it four different ways.

What shape is this? It has four sides, four vertices, but these two sides are the same length.

And these two sides of the same length.

So what shape is this? It is a rectangle.

Now a piece of paper is a rectangle shape.

How many lines of symmetry does a rectangle have and why? It has two lines of symmetry down here, under cross here.

So that means if you folded this shape together, they would look exactly the same.

Now, if you have a piece of paper with you, why not try and folding it diagonally, that way you will see that it is not a line of symmetry.

You will see that it does not match up.

If you do have a piece of paper, you will see when you fold it, that diagonally is not a line of symmetry.

Okay, so I found a rectangle.

This is a rectangle because this side is the same length as this side.

And this site is the same length as this side.

I just found an envelope.

So what I'm going to do is I'm going to show you, folding to show where the lines of symmetry are on a rectangle.

So I can fold it this way.

And look, it is identical.

This side is exactly the same as this side.

Likewise, I can also fold it this way, because if I open up this side is the same as the side.

But what I can't do is fold it diagonally, because look what happens.

Does that look the same? Is that identical? No, it is not.

So if that shows that diagonally is not a line of symmetry.

What shape is this? This shape has three sides, and three vertices, three corners, but also which you may not know, all the lengths are actually the same length.

So what shape is this? This is a triangle, but it's also an equal lateral triangle.

Can you say equal lateral triangle? So an equal lateral triangle is when all the lengths are the same size.

Now how many lines of symmetry do you think this triangle has? Bearing in mind that all the lengths are the same size? So I'm giving you a little bit of a clue here.

That's right, it has three lines of symmetry, one, two, and three.

So that means this side and this side are identical, because of the line of symmetry here.

Well done.

For your independent task, there are five shapes.

For each shape, can you please tell what it is called? How many sides it has? How many vertices it has, and how many lines of symmetry it has? Press play when you are ready for the answers.

Pause the video now.

I'm here with the answers.

Pause the video now to check your answers are the same as mine.

Fantastic work today.

If you would like to share your work with Oak National, then please ask your parent or carer, to share your work on Twitter tagging @Oak National and #LearnwithOak.

You've worked really, really hard today.

Now, let's see what you can remember by completing the quiz on the next page.

Well done for today, bye.