Cambridge International Mathematics

378 Similarity (Chapter 18)

Suppose we enlarge cylinder A to give cylinder B.

End area of B=k^2 £end area of A

) 25 =k^2 £ 9

)^259 =k^2

) k=

q

25

9 =

5

3 fk>^0 g

) k^3 =^12527

) volume of A : volume of B= 27 : 125

EXERCISE 18D

1 For each of the followingsimilarshapes, find the unknown length or area:

ab

cd

2

a the scale factor when enlarging triangle A to give triangle B

b the length of the other two sides of triangle B

c the ratio of their areas.

3 In the given figure, BE=6cm, AE=4cm and ¢ADE

has area 16 cm^2. Find:

a the scale factor to enlarge¢ADE into¢ACB

b the area of¢ABC

c the area of DEBC.

4 In the given figure, AE=3cm, ¢ABE has area 5 cm^2 ,

and BEDC has area 6 cm^2.

Find the length of ED to 3 significant figures.

8cmX

xcmX

6cm 9cm

8cm

40 cmX 20 cmX 6cmX xcm

10 cm

10 cmX

xcm

2cm

4cm

xcmX

24 cmX

A

D

C

B

E

A

B

C

D

E

The side lengths of triangle A are cm, cm and cm. The longest side of a similar triangle B is

cm. Find:

56 7

28 ¡

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Y:\HAESE\IGCSE01\IG01_18\378IGCSE01_18.CDR Monday, 10 November 2008 12:05:33 PM PETER