8.3 B factorising trinomials

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• Middelbare school
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• Leerjaar 3

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You will learn to factorise trinomials.

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Factorise:

5x​2​​−25x

1. 5(x​2​​−5x)
2. x(5x−25)
3. 5x(x−5)
4. (x+5)(x−5)

Simplify:

(x+2)​2​​

1. x​2​​+4
2. 2x+4
3. x​2​​+2x+2
4. x​2​​+4x+4

Simplify:

(x+2)(x+7)

Can we see a relationship between these numbers? Is there a pattern?

(x+2)(x+7)=x​2​​+9x+14

(x+2)(x+7)=x​2​​+9x+14

2+7=9

2⋅7=14

Factorise:

Factorising a trinomial like this will always result in an expression in this form:

x​2​​+10x+16

(x+...)(x+...)

Give the two numbers that make 16 when multiplied and 10 when added.

x​2​​+10x+16

x​2​​+10x+16

x​2​​+10x+16

x​2​​+10x+16

x​2​​+10x+16=(x+...)(x+...)

Factorise:

x​2​​+12x+36

Factorise:

x​2​​−2x−8

Factorise:

x​2​​+x−30

What?	Assignments 67, 68 ,69,71,72,74,C3 (homework for next class)
How?	Work together quietly in pairs. 10 minutes of silence when necessary.
Questions?	No questions for the first minutes, everybody gets started first. While you’re allowed to work together, questions are always first discussed in your pair.
Done?	Assignments 78,79,80,81,82,85
Hint?	Study the examples on page 130.