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Integration of an algebraic and trigonometrical function

  1. Mar 16, 2014 #1
    1. The problem statement, all variables and given/known data
    x
    ∫((x^n)sinx)dx=0.75([itex]\pi[/itex]^2-8) find n if n is a single digit positive integer
    0
    2. Relevant equations

    ∫uv.dx=u∫v.dx-∫(u'.∫v.dx).dx

    3. The attempt at a solution

    i tried putting n=1 or 2 but didnt get the result
    i somehow dont think thats the method
    help please
     
  2. jcsd
  3. Mar 16, 2014 #2
    Hi Arkavo!

    Are you sure about the integration limits? Can you please recheck the question?
     
  4. Mar 16, 2014 #3
    ok no the x is replaced by pi/2
    sorry
     
  5. Mar 16, 2014 #4

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    You need to show your work (as required by PF rules); but first, you need to clarify your question. Do you mean that you want to solve the equation
    [tex] \int_0^x t^n \sin(t) \, dt = \frac{3}{4} \left( \pi^2 - 8 \right) [/tex]
    to find x? Different small integer values of n give different solutions x, so you need to spell out in more detail what you want.

    What was the value of your integral for n = 1 and for n = 2?
     
  6. Mar 16, 2014 #5
    n=3

    NR
     
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