# 2Tvwo § 3.3 Multiplying square roots '19'20

§3.3 Multiplying square roots
However, first there follows a recap on
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Slide 1: Slide
WiskundeMiddelbare schoolhavo, vwoLeerjaar 2

This lesson contains 17 slides, with interactive quizzes and text slides.

Lesson duration is: 50 min

## Items in this lesson

§3.3 Multiplying square roots
However, first there follows a recap on

#### Slide 1 -Slide

Write as short as possible

y=3x62+6x22
A
y=9x42
B
y=9x82
C
y=3x+42
D
Cannot be written any shorter.

#### Slide 2 -Quiz

Which of these does not exist?
A
25
B
25
C
25
D
they all exist

#### Slide 3 -Quiz

Calculate without a calculator

(7)2=

#### Slide 4 -Open question

Recap
- You cannot take the square root of a negative number
So                               is impossible
- You can only add and subtract square roots with the same number or variable underneath the square root sign. Like:

- If you square a square root, you get the number underneath the square root sign (if the square root exists). So for example:
= 7        (this last item is NEW; it's from §3.3 !)

6
5+35=45
(7[?])2

#### Slide 6 -Slide

Multiplying square roots
We've seen that
because:
area of the square =               x            =               = 5

As a rule we say:
5
5
25

#### Slide 7 -Slide

Let's try to find out if you can multiply roots:
Is this true:
x                  =                   ?
ANS
4
9
36

#### Slide 8 -Slide

root 9 x root 4 = root 36
A
this is correct
B
not correct

#### Slide 9 -Quiz

Here you see WHY you can multiply roots:
It is correct to do:
x                  =                    and this is why:
2      x      3         =           6 !
As you see, if you rewrite the roots as numbers, the multiplication is correct!

4
9
36

#### Slide 10 -Slide

Multiplying square roots
If you multiply different square roots, the following rule applies:
(if both square roots exist)

Examples:
(

#### Slide 12 -Slide

root 3 x root 7 =
A
square root 21
B
square root 10
C
21

#### Slide 13 -Quiz

root 18 x root 2 = .....
A
6
B
square root 36
C
square root 20

#### Slide 14 -Quiz

explanation:
x                      =
This is correct, as you may multiply roots!
However, if possible we have to SIMPLIFY, so the best answer is:
= 6 (!), because 6 x 6 = 36
18
2
36
36

#### Slide 15 -Slide

Homework
Make and correct §3.3 (support, standard or challenge)
You may skip 16 and 17.
Later on there follows a little more explanation about
exercises 20 and further.

#### Slide 16 -Slide

Multiplying square roots
If you multiply square root numbers, the following rule applies:
(if both square roots exist)
Examples:     (take note: in the 2nd one there is NO subtraction!)