# Maths Question

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Factorise 9 - 3x - 2x^2 completely.

Should be easy, but I kept ketting stupid things that didn't multiply out to make that. Like (4x - root63 + 3)(4x + root 63 + 3).

Maybe ompleting the square isn't the right way to go, but this doesn't make nice rational numbers.

Should be easy, but I kept ketting stupid things that didn't multiply out to make that. Like (4x - root63 + 3)(4x + root 63 + 3).

Maybe ompleting the square isn't the right way to go, but this doesn't make nice rational numbers.

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#2

Take the negative out to start off with to make it simpler.

2x^2 + 3x - 9 = 0

(2x - 3)(x + 3) = 0

then just put it back in.

(3 - 2x) (x + 3)

2x^2 + 3x - 9 = 0

(2x - 3)(x + 3) = 0

then just put it back in.

(3 - 2x) (x + 3)

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Lol of course. I didn't think to try to factorise after I'd taken the negative out!

Cheers.

Cheers.

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#4

(Original post by

then just put it back in.

(3 - 2x) (x + 3)

**Coran**)then just put it back in.

(3 - 2x) (x + 3)

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You might want to draw the curve from its factorised form or something maybe.

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#6

(Original post by

Why bother putting the negative back in? It gives the same roots anyway

**Pixelfairy #1**)Why bother putting the negative back in? It gives the same roots anyway

though you are right the roots are the same.

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#7

is that really a-level work?

no offence, but it seems pretty easy and its the same as grade b/a gcse work

no offence, but it seems pretty easy and its the same as grade b/a gcse work

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#8

(Original post by

is that really a-level work?

no offence, but it seems pretty easy and its the same as grade b/a gcse work

**MC REN**)is that really a-level work?

no offence, but it seems pretty easy and its the same as grade b/a gcse work

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Yeah I know it's very simple, I've been doing maths all day so my brain has had enough, I think by missing obvious answers it's telling me to stop revising.

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#10

(Original post by

Yeah I know it's very simple, I've been doing maths all day so my brain has had enough, I think by missing obvious answers it's telling me to stop revising.

**mik1a**)Yeah I know it's very simple, I've been doing maths all day so my brain has had enough, I think by missing obvious answers it's telling me to stop revising.

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#11

(Original post by

or telling you to revise more......!

**Katie Heskins**)or telling you to revise more......!

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#12

(Original post by

You'd be suprised what hours of maths can do to the brain!

**bono**)You'd be suprised what hours of maths can do to the brain!

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#13

(Original post by

I find the more maths I do, the more I get into it

**Katie Heskins**)I find the more maths I do, the more I get into it

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#14

(Original post by

Yes i definitely agree - I meant a really long revision session - i.e.) after 4 hours of maths or something.

**bono**)Yes i definitely agree - I meant a really long revision session - i.e.) after 4 hours of maths or something.

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#15

(Original post by

Factorise 9 - 3x - 2x^2 completely.

Should be easy, but I kept ketting stupid things that didn't multiply out to make that. Like (4x - root63 + 3)(4x + root 63 + 3).

Maybe ompleting the square isn't the right way to go, but this doesn't make nice rational numbers.

**mik1a**)Factorise 9 - 3x - 2x^2 completely.

Should be easy, but I kept ketting stupid things that didn't multiply out to make that. Like (4x - root63 + 3)(4x + root 63 + 3).

Maybe ompleting the square isn't the right way to go, but this doesn't make nice rational numbers.

Answer: (2x - 3)(-x - 3) OR (3 - 2x)(x + 3)

To check; either expand to give:

-2x^2 + 3x - 6x + 9

----> -2x^2 - 3x + 9

Which was the original expression you started off with.

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#16

(Original post by

Lol of course. I didn't think to try to factorise after I'd taken the negative out!

Cheers.

**mik1a**)Lol of course. I didn't think to try to factorise after I'd taken the negative out!

Cheers.

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#17

(Original post by

The question posed said factorise so negative needs to be put in to have sussefully factorised the given expression,

though you are right the roots are the same.

**Phil_C**)The question posed said factorise so negative needs to be put in to have sussefully factorised the given expression,

though you are right the roots are the same.

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#18

(Original post by

early a-level work, yes.

**kikzen**)early a-level work, yes.

Year 10 work.

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#19

(Original post by

Why? Either will expand to give the same expression, so you have factorised that expression, whichever you use.

**bono**)Why? Either will expand to give the same expression, so you have factorised that expression, whichever you use.

(2x-3)(x+3) expands to 2x^2 +3x -9 not given in the question,

whilst

(3-2x)(x+3) expands to 9 -3x -2x^2 the expression given.

So the first is wrong in terms of expansion but both do give the same roots, namely -3 and +1.5

Having taken a factor of minus one out of teh original expression, then the correct expression to factorise is:

-{2x^2 +3x -9}

so the answers can be either:

-(2x-3)(x+3) or (3-2x)(x+3) or (2x-3)(-3-x) I would quote the second of the three, it is a neater solution.

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#20

I just put the negative back in because little context was given, it might of been needed to put = y to drawn a graph which would've been upside down if the negatives weren't put back in. There's a lot of transformation work in P1.

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