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Homework Help: Simple integration but i forgot how to do it!

  1. Oct 2, 2005 #1
    Here is my work and problem:

    i made an sign mistake, d/dt (cos t) = -sin(t).http://img101.imageshack.us/img101/561/blah4gk.jpg [Broken]
     
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Oct 2, 2005 #2

    Fermat

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    There's a problem with the link.

    I get document not found
     
  4. Oct 2, 2005 #3
    Ahh sorry!!
    http://img101.imageshack.us/img101/561/blah4gk.jpg [Broken]
     
    Last edited by a moderator: May 2, 2017
  5. Oct 2, 2005 #4

    TD

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    That seems correct, what's the problem? You only forgot the unit vector j I believe.
     
  6. Oct 2, 2005 #5
    oh sorry, i got that answer from someone, but didn't know how they got it! the parts i were i let u = cos (PI t);
    du = -PIsin(PI t);
    -1/PI de = sin(PI t);
    but i don't know how that helps me when i plug it back in!
     
  7. Oct 2, 2005 #6

    TD

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    Just integrate each component. Pi is just a constant, you don't even need a real substitution for it. Do it indirectly by adjusting the dt and correcting in front of the integral.

    [tex]\int {\cos \left( {\pi t} \right)dt} = \frac{1}
    {\pi }\int {\cos \left( {\pi t} \right)d\left( {\pi t} \right)} = \frac{{\sin \left( {\pi t} \right)}}
    {\pi } + C[/tex]
     
  8. Oct 2, 2005 #7
    OHh!! i was making that way more complicated then it should havve been! thanks again TD! :D
     
  9. Oct 3, 2005 #8

    TD

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    No problem :smile:
     
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