Trigonometric substitution for integral with exponential and square root

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Homework Help Overview

The problem involves evaluating the integral \(\int\frac{e^t}{\sqrt{e^{2t}+9}} dt\), which falls under the subject area of calculus, specifically focusing on integration techniques involving trigonometric and hyperbolic substitutions.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts a substitution using \(\tan \theta = \frac{e^t}{3}\) and questions the validity of this approach after receiving feedback from their lecturer. Other participants suggest that both substitutions could be valid but also mention the potential ease of using a hyperbolic substitution instead.

Discussion Status

The discussion is ongoing, with participants providing feedback on the original poster's substitution attempts. Some express that the proposed substitutions seem reasonable, while others indicate that a hyperbolic substitution might be more straightforward. There is no explicit consensus on the correctness of the original approach, but guidance has been offered regarding alternative methods.

Contextual Notes

Participants note the importance of including "dt" in the integral notation, highlighting a common oversight in the original post. The original poster's uncertainty about their lecturer's feedback adds to the discussion's complexity.

annoymage
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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 I am wrong please
 
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Hi annoymage! :smile:

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

Both look ok to me.
 
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.
 
tiny-tim said:
Hi annoymage! :smile:

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

Both look ok to me.


owho, i forgot the "dt" ;P,

Cyosis said:
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 a lot better now, ahahaa
 

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