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If (x+a) is the HCF of x^2 + px + q and x^2 +lx + m then solve for a

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,577

hi Agnishom,

Suppose (x+b) and (x+c) are the other factors of the quadratics.

ie. (x+a)(x+b) = x^2 + px + q

and

(x+a)(x+c) = x^2 + Lx + m

Then

ab = q and ac = m => b = qc/m

also

a+b = p and a+c = L

So substitute for b (in terms of c) and then eliminate c from these equations. Make a the subject of the equation that is left.

Bob

*Last edited by bob bundy (2014-04-07 02:02:46)*

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bob bundy wrote:

So substitute for b (in terms of c) and then eliminate c from these equations. Make a the subject of the equation that is left.

Bob

Can it be done? How?

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,577

Can it be done? How?

Comme si:

Dividing

Also

and

Subtracting

Bob

ps. Not sure what **H**CF means anyway. The above holds for any repeated factor.

You could litter the above with provisos like q ≠ 0, but there's no need as the quadratics 'collapse' if any such conditions fail to apply.

*Last edited by bob bundy (2014-04-07 02:08:08)*

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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Brilliant!

Thank You.

HCF means GCD

'And fun? If maths is fun, then getting a tooth extraction is fun. A viral infection is fun. Rabies shots are fun.'

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,015

Highest common factor, I'd presume?

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,577

HCF means GCD

I worked that out. But what does 'greatest' or 'highest' mean in the context of a factorisation of a quadratic.

(x+a) > (x+b) ?????

I think the question should just read

If (x+a) is a factor of x^2 + px + q and x^2 +lx + m ..............................

Bob

*Last edited by bob bundy (2014-04-07 03:48:45)*

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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**bob bundy****Moderator**- Registered: 2010-06-20
- Posts: 7,577

Yes Highest Common Factor = Greatest Common Divisor. but what's it doing in this question ?

HCF is a significant bit of maths for me. It's when I discovered that I cannot learn anything by hearing it .... I just get audio blindness .......I have to see it. My first high school maths lesson went badly because all the teacher did was talk HCF and LCM and I was hopelessly confused. So I took the text book out for lunch and taught myself what it was all about. It's a milestone in my mathematical education;

ie.

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

In my case it was me that helped me rather than the teacher ..... hope you're still following this ...

Bob

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

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I really do not understand what the dilemma is.

'God exists because Mathematics is consistent, and the devil exists because we cannot prove it'

I'm not crazy, my mother had me tested.

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