2Tvwo § 4.3 Similar figures

• Wiskunde
• Middelbare school
• vwo
• Leerjaar 2

§ 4.3 Similar figures

This lesson:

a. explanation exercise 16

b. new THEORY, about § 4.3

c. more new THEORY, about § 4.3

d. explanation of an exercise from § 4.2?

e. do § 4.3

WHY studying 16 together now?

Because it is the last exercise of the paragraph and, as usual, 

it is a little more difficult than the others.

I noticed that not everybody put in enough effort to crack this one!

Now we do this one together. In future work out all the exercises seriously.

You'll get the chance to key in your answers! And gain points.

But especially: you'll get the chance to learn!

16a

1. 10.8
2. 1.08
3. 0.925
4. 1.80

Explanation exercise 16a:

16 a) The scale factor used to enlarge the height of the photo to the height of the 

screen is 1080 : 1000 = 1.08. 

16b

1. 182
2. 200
3. 1728
4. 192

Explanation exercise 16b:

b) The width of the photo on the screen becomes 1600 x 1.08 = 1728 pixels. 

That strip is 1920 – 1728 = 192 pixels wide. 

Explanation exercise 16c:

16 c) The scale factor used to enlarge the width of the photo to the width of the screen is 1920 : 1600 = 1.2. The height of the photo on the screen would then be 1000 x 1.2 = 1200 pixels. In that case, 1200 - 1080 = 120 pixels would not fit in the height of the screen. 

Time for a Joke?

Always!

After this 'old' exercise plus joke, let's look at §4.3 Similar figures ! 

Theory, part 1.

Use your intuition:
are both shapes similar?

1. yes
2. no

What to do, to prove SIMILARITY of 2 figures ?!

• work on the ANGLES, and
• work on the SIDES
• both are needed, to prove SIMILARITY !
• the next slide explains this more
• because nothing beats an example!

Theory, part 2.

When to DO this?

In exercises 20 and 21 this (complete!) Method is needed.

So, you have to work on both:

• angles, and
• sides
• only then Similarity (or not) has been proved!

Once more:

Are these two shapes SIMILAR, or not?

ANS

SIMILAR, or not?!

1. no
2. yes

Solution: they are NOT SIMILAR!

To prove this, you need to work out:

- are the angles equal?  and

- do the sides have the same RATIO?  Only then you can be sure!

Any questions?

Homework time!

Make, correct, send in pics and make your teacher happy!