2TH §3.4 Calculating using similarity

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§ 3.4 Calculating using similarity

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§3.4: S25, 27, S28

Scale factor and perimeter

Perimeter rectangle A = 2 + 1 + 2 + 1 = 6 cm

Perimeter rectangle B = 4 + 2 + 4 + 2 = 12 cm

Perimeter rectangle C = 6 + 3 + 6 + 3 = 18 cm

Perimeter rectangle D = 8 + 4 + 8 + 4 = 24 cm

12 = 6 x 2; 18 = 6 x 3; 24 = 6 x 4.

The perimeter is multiplied by the scale factor.

Scale factor and area (1)

Rectangles B, C and D are

enlargements of rectangle A.

The scale factors are:

B: 2 (meaning: when you 

multiply length and width of picture

A by 2, you get picture B)

C: 3

D: 4

Scale factor and area (2)

The area is multiplied by the scale factor squared!

Scale factor and area

When the dimensions (length/width/height) of a figure are multiplied by a factor s, the perimeter is also multiplied by s, but the area is multiplied by      .

(When you learn about volume you will find that the volume is multiplied by      )

s​2​​

s​3​​

Homework

• Do §3.4: Exercise 28, 29, 30
• Do §3.5: Exercise 31

• Correct your answers with the Solutionsbook and a red pen
  

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