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Active maths h/w

UhmMaths?! · 2015-10-05 16:49:25

Sorry guys stuck on factorising: Factorise: x^4-7x^2-18

05-10-2015 4:49pm

#1

UhmMaths?!

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Sorry guys stuck on factorising:

Factorise: x^4-7x^2-18

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#2 05-10-2015 4:52pm

spock.

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(x^2 - 9) (x^2 + 2)

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#3 05-10-2015 5:06pm

UhmMaths?!

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Show me how you did it please

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#4 05-10-2015 5:16pm

Pherekydes

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Can you factorise y²-7y-18?

Let y=x²

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#5 05-10-2015 5:22pm

UhmMaths?!

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Y^2-7y-18
(y-9)(y+2)=0
Y=9 or y=-2

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#6 05-10-2015 5:25pm

Pherekydes

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UhmMaths?! wrote: »

Y^2-7y-18
(y-9)(y+2)=0

Yes. Stop here and make the back-substitution x²=y

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