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Homework Help: Definite integral of rational function

  1. Jun 28, 2010 #1
    1. The problem statement, all variables and given/known data

    The definite integral of (t^3 + t -1)/(sin(t)) from 2 to x^2

    2. Relevant equations



    3. The attempt at a solution

    First off, I don't have the solution anywhere, my teacher just gave this to us to work on for the final exam review.

    I can think of a few things. I know for the definite integrals you can first simplify the expression as an indefinite integral, then use the fundamental theorem to solve. I know the integral of 1/sin(t)=ln(sint), and integral of (t^3 + t -1)=(t^4/4 + t^2/2 -t) so for the indefinite integral I have..

    (t^4/4 + t^2/2 -t)ln(sint). do I then just plug in the upper and lower limits to simplify? I kind of feel like I'm on the wrong track because it looks sloppy and usually he gives us problems that have reasonable looking solutions.

    Another attempt is that I recognized 1/sin(t)=csc(t). So then I am left with the integral of (t^3 + t -1)(csc(t))... but I'm not sure if substitution would work.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jun 28, 2010 #2

    Mark44

    Staff: Mentor

    Then you know something that isn't true! You seem to be thinking that
    No, that's not right, either.
     
  4. Jun 28, 2010 #3

    Mark44

    Staff: Mentor

    What is the complete problem statement? I have the feeling that you have omitted an important detail.
     
  5. Jun 28, 2010 #4
    I am sorry but all I have put down is all that's on the paper. Is there more information needed to solve it?
     
  6. Jun 28, 2010 #5

    Mark44

    Staff: Mentor

    The integral you gave looks to be pretty difficult. I have a suspicion that the problem is something like this:
    [tex]f(x) = \int_2^{x^2} \frac{(t^3 + t - 1)dt}{sin(t)}[/tex]
    Find f'(x).​
     
  7. Jun 28, 2010 #6
    yes that is exactly it. Sorry I don't know how to do the Latex.

    This problem is way harder than the others my prof gave us for the final exam review(calculus 1). I guess its possible I wrote it down incorrectly.
     
  8. Jun 28, 2010 #7

    Mark44

    Staff: Mentor

    Whether you know how to use LaTeX or not, you need to give the problem statement exactly as given, which you did not do. If you don't provide the given information we are likely to waste a lot of time trying 1) to solve a different problem than the one that was given, and 2) to solve a problem that is much more difficult than it needs to be.

    You omitted very important information!

    To do this problem you don't need to carry out the integration, but you do need to know about the Fundamental Theorem of Calculus.
     
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