1. ## Integrating e^(-x/45)/45

Okay, so I wasn't sure whether to post this in the stats bit (since this is a CDF I'm trying to find from a given PDF), but I thought since I understand the statistics part of it I'd post it here, since it's the integration I can't seem to do.

$\displaystyle \int\frac{1}{45}e^{-x/45}dx$

I originally got $\displaystyle -e^{-x/45}$ as an answer, but Maple (don't know if people know what that is - just a program that can integrate and do lots of weird stuff really) gave me a different, slightly more complicated answer. Is my answer right?

Actually maybe this should've been put in the stats bit, 'cause I do have a slight problem with the stats reading the question...

2. Originally Posted by chella182
Okay, so I wasn't sure whether to post this in the stats bit (since this is a CDF I'm trying to find from a given PDF), but I thought since I understand the statistics part of it I'd post it here, since it's the integration I can't seem to do.

$\displaystyle \int\frac{1}{45}e^{-x/45}dx$

I originally got $\displaystyle -e^{-x/45}$ as an answer, but Maple (don't know if people know what that is - just a program that can integrate and do lots of weird stuff really) gave me a different, slightly more complicated answer. Is my answer right?

Actually maybe this should've been put in the stats bit, 'cause I do have a slight problem with the stats reading the question...
Both you and Maple are correct.

3. Okay, but I'm stuck on this part of the question (not sure what info you'll need for it 'cause I have no idea)

For this location, find the annual wind wpeed maximum that is likely to be exceeded once every fifty years

4. Originally Posted by chella182
Okay, but I'm stuck on this part of the question (not sure what info you'll need for it 'cause I have no idea)

For this location, find the annual wind speed maximum that is likely to be exceeded once every fifty years
$\displaystyle P(x\geq x_{max})=1-P(x\leq x_{max})=1-\left[1-\exp \left(-\frac{x_{max}}{45}\right)\right]=\exp \left(-\frac{x_{max}}{45}\right)$

The integral you gave is an indefinite one, when it comes to real problems, you need to put the boundary values in, i.e. $\displaystyle =I(x)-I(0)$

5. Originally Posted by chella182
Okay, so I wasn't sure whether to post this in the stats bit (since this is a CDF I'm trying to find from a given PDF), but I thought since I understand the statistics part of it I'd post it here, since it's the integration I can't seem to do.

$\displaystyle \int\frac{1}{45}e^{-x/45}dx$

I originally got $\displaystyle -e^{-x/45}$ as an answer, but Maple (don't know if people know what that is - just a program that can integrate and do lots of weird stuff really) gave me a different, slightly more complicated answer. Is my answer right?

Actually maybe this should've been put in the stats bit, 'cause I do have a slight problem with the stats reading the question...
You are missing the constant of integration, which you will need for this to be a CDF, since you will want the function to go to 1 as x goes to infinity.

Or rather you actualy want:

$\displaystyle \int_0^x \frac{1}{45}e^{-\xi/45}d\xi=1-e^{-x/45}$

CB