# I must have hit my head

1. Sep 12, 2007

because I keep getting jammed up here,

Using u substitution

$$\int \frac{dx}{e^x}$$ I don't see what else to let u equal besides e^x. .....

2. Sep 12, 2007

### learningphysics

Take the denominator to the top...

3. Sep 12, 2007

I just got it I think.....Like I said, somehow since last night I've lost brain cells!:grumpy: for some reason I wouldn't belive that d\dx [e^-x]=e^-x <---
that is correct though right?
what is the derivative of e^-x ?

Last edited: Sep 12, 2007
4. Sep 12, 2007

### learningphysics

almost. be careful about the '-'

You should use the chain rule: what is the derivative of e^(ax)

5. Sep 12, 2007

is it ae^ax ?

so it should be $$-e^{-x}$$

6. Sep 12, 2007