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# Similar Triangles - PowerPoint PPT Presentation

Similar Triangles. Similar shapes. Are Enlargements of each other Corresponding angles are equal Sides are related by the same scale factor. Similar Triangles. Triangles are similar if matching angles remain the same size. 100º. 30º. 50º. 100º. 30º. 50º.

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## PowerPoint Slideshow about 'Similar Triangles' - ondrea

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Presentation Transcript

### Similar Triangles

• Are Enlargements of each other

• Corresponding angles are equal

• Sides are related by the same scale factor

Triangles are similar if matching

angles remain the same size.

100º

30º

50º

100º

30º

50º

10º

50º

120º

120º

10º

50º

5

15

5

4

x 3

x 3

6

Scale factor 3

15

12

1

3

18

Scale factor 1/3

D

E

C

B

Harder example

3

4

6

Triangle ABC is similar to triangle ADE.

DE is parallel to BC.

Calculate the length of BC

4

E

D

Harder example

A

9

6

C

12

B

9

3

x 3

AB & DE are parallel

Explain why ABC is similar to CDE

<CED = <BAC Alternate Angles

5

A

B

<EDC = <ABC Alternate Angles

<ECD = <ACB Vert Opp Angles

3

C

6

E

D

?

Triangle ABC is similar to Triangle CDE

Calculate the length of DE

AC corresponds to CE

Scale Factor = 2

5

A

B

AB corresponds to DE

DE = 2 x AB

3

C

DE = 10cm

6

E

D

?

• To calculate missing sides, we first of all need the scale factor

• We then either multiply or divide by the scale factor

• To show that 2 shapes are similar we can either show that all of the sides are connected by the scale factor or show that matching angles are the same