# Which method do you use to factorise hard quadratics?

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As a tutor I have come across lots of weird and wonderful methods used by students to factorise quadratics where the 'a' coefficient is > 1 e.g.

Which method do you use? Take part in the poll or post below if your method isn't listed - I'm always interested to hear about new methods and it's nice to have all the different methods in one place so students can choose their favourite

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Some brief notes on the methods I've given so you can identify them.

Which method do you use? Take part in the poll or post below if your method isn't listed - I'm always interested to hear about new methods and it's nice to have all the different methods in one place so students can choose their favourite

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Some brief notes on the methods I've given so you can identify them.

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#2

The quadratic formula.

Or is that not GCSE?

Or is that not GCSE?

Last edited by ghostwalker; 11 months ago

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#3

I find inspection works best for me, but the a-levels calculator has given me the luxury of it doing everything for me

We only ever got taught the inspection/trial and error method in school so I find the AC methods really interesting!

We only ever got taught the inspection/trial and error method in school so I find the AC methods really interesting!

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#4

depends on the question. if it says to give to significant figures then i do quadratic formula else i do complete the square or something

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(Original post by

depends on the question. if it says to give to significant figures then i do quadratic formula else i do complete the square or something

**PepeTheFroggi**)depends on the question. if it says to give to significant figures then i do quadratic formula else i do complete the square or something

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#6

(Original post by

I mean if a question just says "factorise this quadratic" so no solving equations.

**Sir Cumference**)I mean if a question just says "factorise this quadratic" so no solving equations.

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#8

**Sir Cumference**)

I mean if a question just says "factorise this quadratic" so no solving equations.

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(Original post by

Don't think mine is listed

First I have to choose the 2 number that make 4x^2 !!!

**Obolinda**)Don't think mine is listed

First I have to choose the 2 number that make 4x^2 !!!

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#10

(Original post by

That's the inspection/trial and error method I mentioned

**Sir Cumference**)That's the inspection/trial and error method I mentioned

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#11

(Original post by

I find inspection works best for me, but the a-levels calculator has given me the luxury of it doing everything for me

We only ever got taught the inspection/trial and error method in school so I find the AC methods really interesting!

**laurawatt**)I find inspection works best for me, but the a-levels calculator has given me the luxury of it doing everything for me

We only ever got taught the inspection/trial and error method in school so I find the AC methods really interesting!

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(Original post by

It won't though and even if it did you can always use the formula and convert your answers. (x - a)(x - b) and multiply up.

**Muttley79**)It won't though and even if it did you can always use the formula and convert your answers. (x - a)(x - b) and multiply up.

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#13

(Original post by

I don't see why a GCSE exam question won't ask a student to factorise a quadratic. Yes that's another method that can be used.

**Sir Cumference**)I don't see why a GCSE exam question won't ask a student to factorise a quadratic. Yes that's another method that can be used.

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(Original post by

Not one with coefficient like that.

**Muttley79**)Not one with coefficient like that.

https://www.ocr.org.uk/Images/528854...er-paper-4.pdf

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#16

(Original post by

We do use the quadratic formula (that's the calculator method) but paper 1 is non calculator so we need to be able to factorise(not just solve) without.

**Obolinda**)We do use the quadratic formula (that's the calculator method) but paper 1 is non calculator so we need to be able to factorise(not just solve) without.

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#17

(Original post by

You can still use the formula without a calculator. The sort of questions that would occur on a non-calculator isn't going to produce surds, you just need proficiency at arithemetic and reasonable knowledge at recognizing perfect squares.

**ghostwalker**)You can still use the formula without a calculator. The sort of questions that would occur on a non-calculator isn't going to produce surds, you just need proficiency at arithemetic and reasonable knowledge at recognizing perfect squares.

Oh and some non-calculator questions may produce surds but the question asks you to solve by completing the square

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#18

I used to use the ‘common’ AC method at gcse, but found it too time consuming when I got to A level. Then I started using the calculator/cheat method, and using the quadratic formula if I didn’t have a calculator (which probably takes even longer).

I can usually do it by inspection now, which I used to find too difficult. I learnt to do it when factorising cubics and quartics.

I can usually do it by inspection now, which I used to find too difficult. I learnt to do it when factorising cubics and quartics.

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#19

(Original post by

E.g 2018 OCR Paper 4 question 16:

https://www.ocr.org.uk/Images/528854...er-paper-4.pdf

**Sir Cumference**)E.g 2018 OCR Paper 4 question 16:

https://www.ocr.org.uk/Images/528854...er-paper-4.pdf

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(Original post by

3 is prime which makes a huge difference - your example did not have that; hence my comment

**Muttley79**)3 is prime which makes a huge difference - your example did not have that; hence my comment

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