Lesson video

Hi everybody, Miss Miles here.

Today before we start our lesson, we're going to start with another did you know fact.

Today's fact is, did you know that if you properly shuffle a deck of cards, the order of the 52 cards that you would have is likely that no other deck of cards in the world has ever been shuffled in that order before.

Quite an interesting one I think.

Okay, back to the maths.

So today, we're going to be completing Lesson Four in our unit of 2D and 3D shape.

And if you haven't completed lessons one, two and three already.

Please make sure you do those first.

Also, before we get started, please ensure that you have completed the pre lesson quiz.

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

Now, let us get started.

In today's lesson, we are going to classify triangles.

Off we go.

So, what are the three different types of triangles? Have a go at drawing them for me.

Pause your video there, and then we'll go through it together.

Off you go.

Okay, let's have a look through the different types of triangles together.

So, this is an equilateral triangle.

An equilateral triangle has all sides that are the same length, and all angles inside are also the same.

You can show that equilateral triangle by looking at the little blue lines on the triangle below.

They're showing you that the sides are all of equal length.

And I find that one easy to remember, because in the title "Equilateral triangle." I can hear the word equal in it, showing me that each of the sizes is of equal length.

And next type is an isosceles triangle.

An isosceles triangle has at least two sides of equal length, and two equal angles.

So this is slightly different to an equilateral triangle in that it has two equal sides.

And again, you can see that on the triangle marked by the two blue lines to show the two sides of equal length.

And we also have scalene triangles.

Scalene triangles have three sides, but all three sides are of different lengths.

And the angles are also of different sizes.

So looking at the images below, we can see that on all of those different triangles, all the sides are of different lengths or all of the angles would also be of different size.

So a question for you to consider now, "can a triangle be a right angled triangle and scalene triangle at the same time?" Remember, a scalene triangle has no sides of equal length and no angles of equal size.

And a right angled triangle, has a right angle within it.

Pause your video now and try to draw a triangle that is both right angle and scalene.

Okay, on your screen now, you can see three different examples of triangles that are both right angled triangles and scalene triangles at the same time.

Did you manage to draw a triangle that was both right angled and scalene? If not, have a go at drawing one of the pictures on the screen and mark the angles and different sides off.

Here we go, showing where our right angles are in those triangles.

So different types of angle now.

So you should have already learned about these different types of angles before.

We have acute angles, right angles, obtuse angles and reflex angles.

Acute angles are angles that are less than 90 degrees.

So if I show a 90 degree right angle with my arms like so, an acute angle is something that is less than that.

So anywhere between a straight line and 90.

Anywhere in between here, so this would be an acute angle, this would also be in acute angle, so is less than 90, a right angle is 90 degrees.

An obtuse angle, is an angle that is between 90 degrees and 180 degrees.

So after our 90 if we continued like so, an obtuse angle would be about that because it is more than 90 but less than 180.

And a reflex angle is an angle between 180 degrees and 360 degrees.

Looking at the triangles below, what types of angles can you spot? Pause the video, draw each of the triangles out and see if you can mark on the different types of angle that we have just discussed.

And here are your answers.

So we can say that in triangle number one, we have a right angle and two acute angles.

Triangle number two also has a right angle and two acute angles.

And triangle number three has a right angle and two acute angles.

Now we've got two other triangles for you to have a look at here.

Again, I would like you to pause the video and see what angles you can spot this time.

Draw them out and mark the different angles on.

Have a go at that for me.

Let's have a look at our answers.

So here, on our first triangle, I can see two very acute angles and one obtuse angle.

And similar to our second triangle, again, two acute angles, and one obtuse angle.

Independent task time now.

Let's apply our learning.

Here we have a variety of different triangles numbered from one to nine.

And what you need to do is sort them into the table at the top.

So you have different criteria to sort these triangles by, you need to sort them into if they're equilateral, isosceles or scalene.

And whether they have all acute angles, one right angle, or an obtuse angle.

You might want to draw the table out in your books.

Or if you want to just have a look at the screen make it a little bit bigger, you can exit the video and click on to the next part of the lesson.

And you can have a look at the worksheet on a fuller screen.

Pause the video there and have a go with that for me.

Now, let's have a look at answers.

How did you get on? Look at the answers on screen and look at the answers that you've written down.

Compare them, how did you get on? Do you need to make any corrections? Okay, well good for completing today's lesson.

Hopefully now you are triangle whizz.

Don't forget to complete the end of lesson quiz.

And hopefully I'll see you again very soon.