Cambridge International Mathematics

368 Similarity (Chapter 18)

Discussion #endboxedheading

² Discuss whether the following pairs of figures are similar:

abc

de f

² Are congruent figures similar?

Consider the enlargement alongside for

which the scale factorkis 1 : 5.

Since k=1: 5 , notice that

A^0 B^0

AB

=

B^0 C^0

BC

=

C^0 D^0

CD

=

D^0 A^0

DA

=

B^0 D^0

BD

=::::=1: 5

Angle sizes do not change under enlargements.

If two polygons aresimilarthen:

² the figures are equiangular and ² the corresponding sides arein proportion.

Example 1 Self Tutor

These figures are similar.

Findxcorrect to 2 decimal places.

Since the figures are similar, their corresponding sides are in the same ratio.

)

x

4

=

5

3

) x=^53 £ 4

) x=^203

)

A

B

C

D

A'

B'

C'

D'

3cm

4cm

xcm

5cm

x¼ 6 : 67

IGCSE01

cyan magenta yellow black

(^05255075950525507595)
100 100
(^05255075950525507595)
100 100
y:\HAESE\IGCSE01\IG01_18\368IGCSE01_18.CDR Wednesday, 8 October 2008 10:07:45 AM PETER