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Homework Help: Trigonometric substitution

  1. Apr 26, 2010 #1
    1. The problem statement, all variables and given/known data

    Evaluate [tex]\int[/tex][tex]\frac{e^t}{\sqrt{e^2^t+9}}[/tex]

    2. Relevant equations


    3. The attempt at a solution

    i'm using substitution

    tan [tex]\theta[/tex] = [tex]\frac{e^t}{3}[/tex]

    or i also can use

    tan [tex]\theta[/tex] = [tex]\frac{3}{e^t}[/tex]

    both will get the same answer.

    am i right? because my lecturer told i was wrong, i'm really sure that i did right..
    can anyone help me if im wrong please
  2. jcsd
  3. Apr 26, 2010 #2


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    Science Advisor
    Homework Helper

    Hi annoymage! :smile:

    (never leave out the "dt" after an ∫ :wink:)

    Both look ok to me.
  4. Apr 26, 2010 #3


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    Homework Helper

    It is a possible substitution, but I can't tell you what's wrong until you show your work. That said using a hyperbolic substitution is a lot easier than the one you did.
  5. Apr 26, 2010 #4
    owho, i forgot the "dt" ;P,

    i guess this what my lecturer wanted me to do (hyperbolic),

    k thanks tiny-tim and cyosis, i fell alot better now, ahahaa
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