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# C4 Binomial 8 mark question. Tweet

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1. C4 Binomial 8 mark question.
Find the coefficient of x^2 in ascending powers of x in terms of a

√(1 + ax)/(4-x)

So i split it into

(1 + ax)^1/2 multiplied by
(4-x)^-1/2 --> which then i simplified to 4^-1/2 x (1-x/4)^-1/2

So now i have..

(1 + ax)^1/2 x [1/2 x (1-x/4)^-1/2]

So i have expanded both brackets out only up until the coeffecients of x because i knew i'd be timing them out in the end which then i should get x^2..

(1 + ax)^1/2 = 1 + (ax)/2
[1/2 x (1-x/4)^-1/2] = 1/2 - x/16

I multipled them together and got = 1/2 - x/16 + (ax)/4 - (ax^2)/32..

It came out to be wrong i think, according to the MS and it looks confusing on the MS too.. and sorry if my working out looks confusing, i don't have latex

Here's the paper (Q6 and MS)

Thanks.

P.S Where did i go wrong?
Last edited by jameslad; 17-06-2012 at 01:28.
2. Re: C4 Binomial 8 mark question.
Find the coefficient of x^2 in ascending powers of x in terms of a

√(1 + ax)/(4-x)

So i split it into

(1 + ax)^1/2 multiplied by
(4-x)^-1/2 --> which then i simplified to 4^-1/2 x (1-x/4)^-1/2

So now i have..

(1 + ax)^1/2 x [1/2 x (1-x/4)^-1/2]

So i have expanded both brackets out only up until the coeffecients of x because i knew i'd be timing them out in the end which then i should get x^2..

(1 + ax)^1/2 = 1 + (ax)/2
[1/2 x (1-x/4)^-1/2] = 1/2 - x/16

I multipled them together and got = 1/2 - x/16 + (ax)/4 - (ax^2)/32..

It came out to be wrong i think, according to the MS and it looks confusing on the MS too.. and sorry if my working out looks confusing, i don't have latex

Here's the paper (Q6 and MS)

Thanks.

P.S Where did i go wrong?
Expand both brackets till term.

Then multiply them.

The answer will be the coefficient of term.

So you will get,

Last edited by raheem94; 17-06-2012 at 02:04.
3. Re: C4 Binomial 8 mark question.
and sorry if my working out looks confusing, i don't have latex
You do. http://www.thestudentroom.co.uk/wiki/LaTex
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