This lesson contains 14 slides, with interactive quiz and text slides.

Lesson duration is: 50 min

Items in this lesson

§ 4.4 Calculating using similarity

That's the content for today!

Slide 1 - Slide

Calculating unknown sides in similar figures

When calculating unknown sides in similar figures, you can use the scale factor (see LessonUp §4.2).

To make it easier to find out which sides are corresponding sides, you should sketch both figures in the same position.

Watch the following example!

Slide 2 - Slide

Example

Triangle ABC and triangle PQR are similar figures. Calculate the length of AC and PR.

Slide 3 - Slide

Sketch

Here a better sketch

is added.

Now the triangles

are in the same position.

Slide 4 - Slide

Calculations

Slide 5 - Slide

Before we go on ...

here comes a non-math slide !

Slide 6 - Slide

Slide 7 - Slide

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.

Slide 8 - Slide

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

Slide 9 - Slide

Scale factor and area (2)

The area is multiplied by the scale factor squared!

Slide 10 - Slide

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 )

s2

s3

Slide 11 - Slide

Homework

Make §4.4:

Support: 24, 25, S26, 27, S28, 28, 29

Standard: 24, 25, 26, 27, 28, 29, 30

Challenge: 24, 26, 27, 28, 29, 30, C5

Correct your answers with the Solutionsbook and a red pen