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Homework Help: Trouble with tables

  1. Oct 5, 2013 #1
    1. The problem statement, all variables and given/known data

    Hi I have a broad quesiton. I'm trying to make something fit the form of something in one of the tables in my book I can't seem to quite make it.
    integral (1/2x^3 - 3x^2) dx

    2. Relevant equations

    3. The attempt at a solution

    I just messed with the denomator.

    I can't find something in the tables that fits this. Does anyone have any ideas?
  2. jcsd
  3. Oct 5, 2013 #2
    You can write the given integral as:
    $$\int \cfrac{dx}{x^2\cdot x\left(2-\cfrac{3}{x}\right)}$$
    A substitution would make it very easy. It is easy to spot.
  4. Oct 5, 2013 #3
    I'm sorry I still don't see it. Sub for u = x^2?
  5. Oct 5, 2013 #4
    You have x^2 in the denominator i.e 1/x^2. This is the derivative of something very familiar. :rolleyes:
  6. Oct 5, 2013 #5


    Staff: Mentor

    What you wrote is this:
    $$ \int \frac 1 2 x^3 - 3x^2 dx$$

    To indicate that 2x3 - 3x2 is in the denominator, put parentheses around the denominator, not the whole fraction, like this 1/(2x3 - 3x2).
  7. Oct 5, 2013 #6

    Ray Vickson

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    Science Advisor
    Homework Helper

    Partial fractions.
  8. Oct 5, 2013 #7
    No sure. This would be -1/x whose derivavite is is 1/x^2 are you thinking ln of something? Ray says partial fractions but this is the section where you have to look them up in tables.
  9. Oct 5, 2013 #8
    Yes, use the substitution 1/x=t.

    Partial fractions can also be used.
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