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Homework Help: Evaluating line integrals

  1. Mar 9, 2008 #1
    [SOLVED] Evaluating line integrals

    1. The problem statement, all variables and given/known data
    I am given a line integral:

    [tex]\int (x^2+y^2)^2ds[/tex], where C is a circle of radius 3 with centre in (0;0).

    Evaluate it.

    3. The attempt at a solution
    Ok, first I know [tex](x^2+y^2)^2[/tex] = [tex]81[/tex]. So far, so good.

    Then I know for an object in the xy-plane, ds = r*dr*d[tex]\theta[/tex]. I just insert and use the correct limits, and do the integral?

    Thanks in advance.
  2. jcsd
  3. Mar 9, 2008 #2
    No, I am totally wrong.

    ds is _not_ what I wrote above, but ds = |r'(t)|dt.
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