Lesson video

Hi, I'm Miss Davies, and in this lesson we're going to be enlarging shapes by positive scale factors.

Enlargements occur when a shape gets bigger and bigger again.

Notice that all of the sides have been made bigger by the same scale factor.

This means that all of the lengths have been multiplied by the same number.

This is also an enlargement.

However, the scale factor is less than one, because the shape has gotten smaller.

To identify the scale factor that shape A has been enlarged by to give shape B, we need to look at the corresponding lengths.

The width of shape A is four squares.

This has been multiplied by three to give the width of shape B.

The height of shape A is two squares.

This has been multiplied by three to give the height of shape B.

Therefore the scale factor of shape A to shape B is three.

The scale factor from shape B to shape A is the reciprocal of this.

Shape B has been divided by three to give shape A.

We write this as a scale factor of 1/3, as it is 1/3 the size.

We've been asked to enlarge this triangle by a scale factor of four.

We're going to start by looking at the base.

The base of this triangle is four squares.

So the enlarged shape will have a base of 16 squares.

The height of this triangle is two.

When this is enlarged by a scale factor of four, the height of the new triangle will be eight.

This is our enlarged triangle.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Here are the answers.

Shape D has a base of eight squares and a height of four squares.

Because shape A has got a base of two, if we multiply that by four, it gives us eight.

Shape A has got a height of one square, when multiplied by four, this gives a height of four squares.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Here are the answers.

The enlarged images can be positioned anywhere on the grid.

Make sure that you've multiplied all lengths by the same scale factor for each shape.

Here is a question for you to try.

Pause the video to complete your task and resume once you're finished.

Here is the answer.

Jon hasn't multiplied all of the lengths by the same scale factor.

This has meant that the top vertex is in the wrong position.

With this question we are enlarging the triangle by a scale factor of 2.

5.

We start by looking at the base.

This is four squares.

Four multiplied by 2.

5 is 10, so the base of the enlarged shape is going to be 10 squares.

The height of our triangle is three squares.

Three multiplied by the scale factor of 2.

5 is 7.

5, so the height of our enlarged triangle is 7.

5 squares.

This is our enlarged triangle.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Here are the answers.

In part b, because the scale factor is 1/3, the enlarged shape is smaller than the original.

This always happens if the scale factor is between zero and one.

That's all for this lesson.

Thanks for watching.