Lesson video

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Hello, and welcome to this lesson on lines of symmetry with me, Miss Oreyomi.

As usual, you'll be needing a paper and a pen.

You might also be needing a pencil in this lesson, 'cause you will be drawing.

So please get that if you do not have it.

So pause the video now.

Go get your equipment, and when you're ready, press play to continue with the lesson.

Okay, in this lesson, you will be able to identify and count the lines of symmetry for a shape.

Your first task, then, is how many pentagons can you draw on a three-by-three grid? So in your book, I want you to draw as many three-by-three grids as you possibly can.

And then how many different pentagons can you draw on a three-by-three grid? So pause the video now and attempt the task.

And then when you're ready, resume to continue the lesson.

These are examples of the different types of pentagon that you could have drawn on a three-by-three grid.

How would you define line of symmetry? If someone comes up to you today and say, "Hey, how would you describe line of symmetry?" What would you tell them? Let's look at the two shapes we have on our screen right now.

I am going to illustrate what a line of symmetry is.

And whilst I'm doing that, can you think of a way to define what line of symmetry is? So the first shape.

Got a line there, and I've got another one there, and I'm telling you these are my lines of symmetry for this shape.

So I've got one line of symmetry here and my second line of symmetry here.

Okay, so that's for shape one.

What of shape two? Got one there, another one there, and a third one there.

Okay, are you getting an idea of how you can define line of symmetry? I have written, and your definition could be different from mine, I have written that a line of symmetry is found when you can fold a shape onto another shape in half so that it fits exactly on top of the other.

Then we can say that shape has got one line of symmetry or two lines of symmetry.

So in this case, if I fold this shape in half, that would give me one line of symmetry.

And if I fold it this way, I could get my second line of symmetry.

Looking at this shape here, I could fold it this way, this way, and that way to get my three lines of symmetry.

Now, what are some features of our lines of symmetry? Well, from here, you can see that they all intersect at a point.

They all intersect at a point, so lines of symmetry on a shape intersect at a point.

Also, when they reflect, they have the same distance.

So the reflection is my shape is split in two from here, and there's the same distance from this point here to my line of symmetry, and from this line of symmetry to my edge of the shape.

And you can see the same here.

This shape is reflected along this line of symmetry, and the shape is equal from this edge to the line of symmetry and from the line of symmetry to this edge.

This is a neater version of what I just explained.

So we can see that they all intersect at a given point.

And in this case, this distance and that distance are the same, and the distance from this edge to the line of symmetry and then from the line of symmetry to the other end is the same.

And we could do the same for this here, and for this here.

So I want you to pause the video now and attempt your independent task.

When you're done with that, press resume, and we will carry on with the lesson.

Okay, let's go over our answers.

All the polygons below have equal sides.

They are equilaterals.

How many lines of symmetry does each shape have? The answers are in red, and I've just given a quick sketch of number seven, the lines of symmetry for number seven.

Next one, write down the mathematical name for each of these triangles.

This is an isosceles triangle, because both sides are equal.

This is a right-angled triangle.

It could also be called scalene.

This is an equilateral triangle.

A right-angled isosceles triangle.

So I had provided you with three examples of the resulting shape when you fold a square piece of paper in half, and then you fold it in half again along the lines of symmetry.

Did you get the same shapes that I did, or did you get different ones? Right! You have now reached the end of this lesson on lines of symmetry.

Good job on sticking right through the end, and I hope to see you at the next lesson.