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Breaking a fraction down to a sum of fractions

  1. Jul 30, 2008 #1
    1. The problem statement, all variables and given/known data
    Re-write the following fraction into the sum of fractions:
    1/[(n^3)+n]


    2. Relevant equations
    None that I can think of. . .


    3. The attempt at a solution
    I first changed [(n^3)+n] to n[(n^2)+1], so by the rules, the aformentioned fraction should equate to (A/n) + (B/[(n^2)+1]). That means A * [(n^2)+1] + B * n should equate to 1. This is where I run into problems. Since there's only one n^2, that means A should equate to zero. However, there's also the constant A, which should equate to one. 0 doesn't equate to one. Is the problem faulty or am I missing something?
     
  2. jcsd
  3. Jul 30, 2008 #2

    Defennder

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    Homework Helper

    If the quadratic term in the denominator cannot be decomposed into linear factors, then the numerator should be given the form Ax+B instead, rather than just A.
     
  4. Jul 30, 2008 #3
    1/[(n^3)+n] = 1 / (n)(n^2 + 1)
    = 1 + n^2 - n^2 / (n)(n^2 + 1)
    = (1/n) - [n/(n^2 +1)]
     
  5. Jul 30, 2008 #4
    @poster - the method u used is only valid for two linear expressions' product, but for your one you'll have to use Bn instead of just B.
     
  6. Jul 30, 2008 #5
    ARGH! Totally forgot that! Thanks!!
     
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