How can I derivate this?

• Dec 14th 2011, 10:10 AM
gotmejerry
How can I derivate this?
$e^{-x}}\sum _{k=0}^{2011}{\frac {{x}^{k}}{k!}$
Thank you!
• Dec 14th 2011, 10:15 AM
Siron
Re: How can I derivate this?
Use the product rule and:
$\frac{d}{dx}\left(\sum_{k=0}^{2011} \frac{x^k}{k!}\right)=\sum_{k=0}^{2011} \frac{d}{dx}\left(\frac{x^k}{k!}\right)$
• Dec 14th 2011, 01:22 PM
gotmejerry
Re: How can I derivate this?
OKay, but i dont know how to derivate that factorial stuff
• Dec 14th 2011, 01:26 PM
pickslides
Re: How can I derivate this?
You are only taking the derivative with respect to x, k! is constant.
• Dec 14th 2011, 01:47 PM
gotmejerry
Re: How can I derivate this?
Then it is only kx^k-1 /k!?
• Dec 14th 2011, 01:52 PM
e^(i*pi)
Re: How can I derivate this?
Quote:

Originally Posted by gotmejerry
Then it is only kx^k-1 /k!?

$\frac{kx^{k-1}}{k!}$ is correct, however, you can use your definition of a factorial to cancel a factor of k giving $\dfrac{x^{k-1}}{(k-1)!}$

But don't forget your other term and use the product rule
• Dec 14th 2011, 01:56 PM
gotmejerry
Re: How can I derivate this?
Thank you!