# Homework Help: Trigonometric substitution

1. Apr 26, 2010

### annoymage

1. The problem statement, all variables and given/known data

Evaluate $$\int$$$$\frac{e^t}{\sqrt{e^2^t+9}}$$

2. Relevant equations

N/A

3. The attempt at a solution

i'm using substitution

tan $$\theta$$ = $$\frac{e^t}{3}$$

or i also can use

tan $$\theta$$ = $$\frac{3}{e^t}$$

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. Apr 26, 2010

### tiny-tim

Hi annoymage!

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

Both look ok to me.

3. Apr 26, 2010

### Cyosis

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. Apr 26, 2010

### annoymage

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