Results 1 to 3 of 3

Math Help - Partial fractions

  1. #1
    Member
    Joined
    Dec 2008
    Posts
    105

    Partial fractions

    I'm stuck on b) iii) of this question. I'll show you what i have got so far.

    the function f is given by f(x)= \frac{9}{(1+2x)(4 - x)}

    a) express f(x) as a partial fraction.

    I got \frac{2}{(1+2x)} + \frac{1}{(4 -x)}

    b) i) Find the first three terms in the expansion of \frac{1}{4 -x}

    I got \frac{1}{4} + \frac{x}{16} + \frac{x^2}{64}

    b) ii) Obtain a similar expansion for \frac{1}{1+2x}

    I got 1 - 2x + 4x^2

    where i am stuck on is b) iii)

    Hence, or otherwise, obtain the first three terms in the expansion of f(x) in ascending powers of x
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Grandad's Avatar
    Joined
    Dec 2008
    From
    South Coast of England
    Posts
    2,570
    Hello Beard
    Quote Originally Posted by Beard View Post
    I'm stuck on b) iii) of this question. I'll show you what i have got so far.

    the function f is given by f(x)= \frac{9}{(1+2x)(4 - x)}

    a) express f(x) as a partial fraction.

    I got \frac{2}{(1+2x)} + \frac{1}{(4 -x)}

    b) i) Find the first three terms in the expansion of \frac{1}{4 -x}

    I got \frac{1}{4} + \frac{x}{16} + \frac{x^2}{64}

    b) ii) Obtain a similar expansion for \frac{1}{1+2x}

    I got 1 - 2x + 4x^2

    where i am stuck on is b) iii)

    Hence, or otherwise, obtain the first three terms in the expansion of f(x) in ascending powers of x
    But you've done all the hard work! - and you've done it right so far. You're going to kick yourself, I think, because all you need to do is to use your Partial Fractions answer:

    f(x) = 2(1+2x)^{-1} + (4-x)^{-1}

    together with your answers to b(i) and b(ii) to write the answer down. Can you see it now?

    Grandad
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Dec 2008
    Posts
    105
    I don't feel too bad considering I haven't done this thing for ages but it was a nice little reminder. Thanks.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 0
    Last Post: April 28th 2010, 09:53 AM
  2. Partial Fractions
    Posted in the Pre-Calculus Forum
    Replies: 2
    Last Post: February 4th 2010, 06:24 PM
  3. Partial Fractions
    Posted in the Pre-Calculus Forum
    Replies: 9
    Last Post: January 17th 2010, 02:20 AM
  4. Help on Partial Fractions
    Posted in the Calculus Forum
    Replies: 12
    Last Post: January 6th 2010, 03:00 AM
  5. partial fractions
    Posted in the Algebra Forum
    Replies: 1
    Last Post: January 21st 2007, 04:49 AM

Search Tags


/mathhelpforum @mathhelpforum