**Similarity**

Starter

Main Activity

**L.O. Find the scale factor between two similar shapes and use it to find missing lengths.**

Rectangle B is a enlargement of rectangle A.

A

6 cm

15 cm

What is the scale factor of the enlargement?

Calculate the width of B.

B

4 cm

Starter

Rectangle B is a enlargement of rectangle A.

A

6 cm

15 cm

What is the scale factor of the enlargement?

2.5

Calculate the width of B.

10 cm

B

4 cm

Example

Triangle B is similar to triangle A.

6 cm

5 cm

20 cm

a

b

13

1

3

Find the values of a and b.

Example

Triangle B is similar to triangle A.

6 cm

5 cm

20 cm

a = 16

b = 4 cm

13

1

3

Find the values of a and b.

x 3

1

3

2

3

A and L - S.F.

B and N - S.F. 0.4

C and M - S.F.

D and K - S.F. 1

E an P - S.F. 1.6

F and Q - S.F. 1.2

G and R - S.F. 1

H and S - S.F

2

3

2

3

1

3

1

3

15

16

Main Activity 2

Find the value of each letter in the diagrams.

Main Activity 2

Find the value of each letter in the diagrams.

x = 8, y = 5

1

3

a = 8, b = 16

a = 40, b = 28.8

x = 28, y = 26.25

y = 10

a = 2.4

**Activities**

**Activity**

Answers

Answers

**Key**

Examples

Examples

**Worked**

Example

Example

Similar Shapes

Two shapes are similar if one is an

enlargement of the other.

Are these shapes similar?

5 cm

7 cm

10 cm

12 cm

6 cm

8.54 cm

Are these shapes similar?

5 cm

7 cm

10 cm

12 cm

6 cm

8.54 cm

No because:

12/10 = 1.2

6/5 = 1.2

8.54/7 = 1.22

**Worked**

Example

Example