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Homework Help: Limits of integration

  1. Dec 9, 2012 #1
    My limits of integration for my angle I chose to be from pi to 0 then I got the negative answer from what was in the book.. Shouldn't that be correct because we are integrating from -3 to 3?
     

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  3. Dec 10, 2012 #2

    Mark44

    Staff: Mentor

    What did you get for your answer? I got a positive value for the integral, a tad over 3.
     
  4. Dec 10, 2012 #3
    when I integrated from pi to 0 I got 1/2pi(cos(9) - 1)
     
  5. Dec 10, 2012 #4

    Mark44

    Staff: Mentor

    That should be -(1/2)pi *(cos(9) - 1). The antiderivative of sin(u) is -cos(u).
     
  6. Dec 10, 2012 #5
    So it is correct to integrate from pi to 0?
     
  7. Dec 10, 2012 #6

    Mark44

    Staff: Mentor

    It's correct to integrate from 0 to pi, like so:
    $$ \int_{\theta = 0}^{\pi} \int_{r = 0}^3 sin(r^2)r~dr~d\theta$$

    Is that what you meant? If you meant ##\pi## as the lower limit of integration, and 0 as the upper limit, you'll get the opposite value.
     
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