I think my problem solving is absurd.

1. Nov 28, 2009

stanton

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

Evaluate the definite integral:

2. Relevant equations

$$\int u^n du/dx$$ = u^(n+1)/(n+1) (n not equal to -1)

3. The attempt at a solution

(-1) muliplied by $$\int$$ (e^-x +2)^-1 (-e^-x) dx = ?

and if I follow the equation above, I got denominator zero, for I broke the rules 'n is not equal to zero'
I think I did as the equation. but now what should I do now?

2. Nov 28, 2009

Do you know how to integrate

$$\int \frac 1 u \, du$$
?

3. Nov 29, 2009

tnutty

Let u = e^(-x) + 2
the du = ...

4. Nov 29, 2009

stanton

-e^(-x)

5. Nov 29, 2009

So with $$u = e^{-x} + 2$$ and $$du = -e^{-x}$$, what happens to your integral?

6. Nov 30, 2009

stanton

Thank you for your help. I did like this:

Can you check is this the right answer?

7. Nov 30, 2009

Looks good. You are correct that the absolute value signs are not needed in the answer, since $$e^{-x} + 2$$ is never negative.