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# C4 Binomial problem

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1. C4 Binomial problem
Im not sure how to go about answering this question/ where im going wrong.

5 A) Write down the first 3 terms in the binomial expansion of in ascending power of x.

5 B) By choosing suitable values of n and x, use the series to find the cube root of 1003 to 9 signifigant figures.

For part A i obtained the first 3 terms to be

For part B I assume n is 1/3 and x = 334, as 1003 - 1 = 1002 and 1002 / 3 = 334 so i substitute x as 334 later.

So i get

I expand it to 3 terms and get

I put substitute 334 as x and get -111,221. , as i get more terms of x the answer seems to deviate further?
Last edited by ch0wm4n; 01-04-2012 at 18:00. Reason: Made a typo :(
2. Re: C4 Binomial problem
3. Re: C4 Binomial problem
I think it hasnt worked because that binomial expansion is only valid for |x|<1

Im going to have to think about how to actually do it though :L

edit:
(Original post by Mr M)
just a typo i think - the answer -111,221 comes from the expansion with the correct sign
Last edited by just george; 01-04-2012 at 17:15.
4. Re: C4 Binomial problem
(Original post by just george)
I think it hasnt worked because that binomial expansion is only valid for |x|<1

Im going to have to think about how to actually do it though :L

edit:
just a typo i think - the answer -111,221 comes from the expansion with the correct sign

How would finding the expansion of 1.003^(1/3) help?
5. Re: C4 Binomial problem
(Original post by Mr M)
(Original post by ch0wm4n)
Im not sure how to go about answering this question/ where im going wrong.

5 A) Write down the first 3 terms in the binomial expansion of in ascending power of x.

5 B) By choosing suitable values of n and x, use the series to find the cube root of 1003 to 9 signifigant figures.

For part A i obtained the first 3 terms to be

For part B I assume n is 1/3 and x = 334, as 1003 - 1 = 1002 and 1002 / 3 = 334 so i substitute x as 334 later.

So i get

I expand it to 3 terms and get

I put substitute 334 as x and get -111,221. , as i get more terms of x the answer seems to deviate further?
(Original post by just george)
I think it hasnt worked because that binomial expansion is only valid for |x|<1

Im going to have to think about how to actually do it though :L

edit:
just a typo i think - the answer -111,221 comes from the expansion with the correct sign
Here's how to do it:

Multiply both sides by 10

Substitute x=0.001 and n=1/3

OP, you got the wrong answer because this expansion is only valid for,

Hope it helps .
Last edited by raheem94; 01-04-2012 at 17:25.
6. Re: C4 Binomial problem
(Original post by Mr M)

How would finding the expansion of 1.003^(1/3) help?
Ah thats it

then you can go from there ch0wm4n?
Last edited by just george; 01-04-2012 at 17:25.
7. Re: C4 Binomial problem
You have made over 1,500 posts raheem so you must know you have just broken the Forum Rules.
8. Re: C4 Binomial problem
(Original post by Mr M)
You have made over 1,500 posts raheem so you must know you have just broken the Forum Rules.
Actually, i do know the rules, i didn't meant to break them.

That's why i didn't substituted the values in the RHS so that the OP does it himself.

I just showed him how to manipulate the LHS to get the answer, my post is only so big, looking like a solution, because i tried to show each step so that he doesn't get confused.

I apologise if you think i was wrong.
9. Re: C4 Binomial problem
(Original post by raheem94)
Here's how to do it:

Multiply both sides by 10

Substitute x=0.001 and n=1/3

OP, you got the wrong answer because this expansion is only valid for,

Hope it helps .

(Original post by just george)
Ah thats it

then you can go from there ch0wm4n?

(Original post by Mr M)

How would finding the expansion of 1.003^(1/3) help?
Thanks for the help guys .

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Last updated: April 2, 2012
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