1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Integration by parts of a function

  1. Feb 2, 2010 #1
    the function is c = 15te-.2t

    the goal is to integrate it from t = 0 to t = 3

    so to set up the integral i took out the 15 first so i got:

    15 * integral from 0 to 3 of t*e-.2t

    i set u = t and so du = dt
    dv = e-.2tdt so v= -5e-.2t

    so following the integration by parts formula i got:

    15(-5*e-.2t + 5* integral of e-.2tdt

    then after integrating the second part i got

    15(-5e-.2t - 25e-.2t) evaluated from 0 to 3

    when evaluated i got

    (-123/4826181 - 205.8043635)-(-75-375) = 120.7130184

    but thats wrong,

    anyone have any hints or sees any mistakes that i made?

    thanks
     
  2. jcsd
  3. Feb 2, 2010 #2

    rock.freak667

    User Avatar
    Homework Helper

    this should be

    15(-5te-0.2t+5∫e-.2tdt
     
  4. Feb 2, 2010 #3
    your right, thats just a typo, i had the t there in my calculations
     
  5. Feb 2, 2010 #4

    rock.freak667

    User Avatar
    Homework Helper

    it looks like you did it correct, is your answer supposed to be in terms of e?
     
  6. Feb 2, 2010 #5
    i dont think so, it just asks for the exact answer
     
  7. Feb 2, 2010 #6

    rock.freak667

    User Avatar
    Homework Helper

    Then you need to write it in terms of the constant e. So recalculate the answer, just not using a calculator.
     
  8. Feb 2, 2010 #7
    so just leave it as with the base e but calculate the exponents of e?
     
  9. Feb 2, 2010 #8

    rock.freak667

    User Avatar
    Homework Helper

    Yes.
     
  10. Feb 2, 2010 #9
    ok, thanks alot
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook