Trigonometric substitution

  • Thread starter annoymage
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  • #1
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Homework Statement



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

Homework Equations



N/A

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
 

Answers and Replies

  • #2
tiny-tim
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Hi annoymage! :smile:

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

Both look ok to me.
 
  • #3
Cyosis
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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.
 
  • #4
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Hi annoymage! :smile:

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

Both look ok to me.

owho, i forgot the "dt" ;P,

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.

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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