Binomial % Error & Estimate..

Hi,

I have completed a binomial expansion from the Edexcel Jan 2009 C4 paper. Question 3, part B says to expand f(x) in ascending powers of x, up to and including the term

x^2

. I have done this and get :

4 + 0x + 9\frac{3}{4}x^2

part c reads 'Find the percentage error made in using the series expansion in part (b) to estimate the value of f(0.2). Give your answer to two significant figures.

I don't really have a clue what to do..

Thanks for any help :smile:

Reply 1

Maniachris

1

well just sub in 0.2 into each expression and work them out using your calc. then divide the binomial value by the actual value and times by 100 to work out what percentage the expansion value is of the actual value, then subtract this from 100 to get the error.

Reply 2

Danielisew

OP

1

I subbed 0.2 into the function, which was :

4/(3x+2)^2 + 3/(1-x)

found by using partial fractions. (There was another bit but you had to prove that A - the numerator was equal to zero therefore it cancels out). I get 10.51. I then sub 0.2 into my expansion and get 4.39. These values are unusually far apart - is this correct?

Reply 3

ghostwalker

17

Danielisew

I subbed 0.2 into the function, which was :

4/(3x+2)^2 + 3/(1-x)

found by using partial fractions. (There was another bit but you had to prove that A - the numerator was equal to zero therefore it cancels out). I get 10.51. I then sub 0.2 into my expansion and get 4.39. These values are unusually far apart - is this correct?