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Sapphire_Frenzy's avatar

(3) Algebra Problem: Can you help?

Asked by Sapphire_Frenzy (90 points ) October 9th, 2012

The question is:

3. Factorise 12ab – 18a2

and the answers are:

1. 3b(4b – 6a)
2. 6a(2b – 3a)
3. 2a(6a – 3b)

Can anyone help me please with how to GET to the answer?

So far I’ve tried finding the factors which multiply to make minus 18 but nothing I’ve found adds up to make positive twelve. Also the answer is arranged completely differently to the (x+yada)(x+yada) that i’m used to.

Thank you

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6 Answers

Sapphire_Frenzy's avatar

No matter, I’ve figured it out

zenvelo's avatar

The question you should be asking are:

What is the greatest common factor to 12 and 18? don;t get hung up on the sign.

What is a common denominator to ab and a^2 ?

divide by those two factors combined, and you’ll get your answer.

Sapphire_Frenzy's avatar

It’s 2

I worked backwards from the answer instead.

Sapphire_Frenzy's avatar

@zenvelo I’ll make a note of your approach to help me with similar questions. Thank you.

CWOTUS's avatar

May I suggest that you learn the correct notation for this problem.

You’re looking for the factors of:
12ab – 18a^2
not
12ab – 18a2

The term “a-squared” is written in formats such as this (and Excel spreadsheets, too) as
a^2

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