- #1
clumps tim
- 39
- 0
HI people,
I was trying to derive the stefan-boltzman law from the planc's formula, I kind of got stuck with an integral
$$ \int_{0}^{\infty} \frac{x^3}{e^x -1} dx $$
I tried simplifying it with
$$ \int_{0}^{\infty} x^3 e^{-x} \sum_{n=0}^{\infty} e^{-nx} dx $$
Now I don't know what to do with the summation. I could evaluate
$$ \int_{0}^{\infty} x^3 e^{-x} dx = 6$$
pleas help me to get the rest of it, I see the answer comes with $\pi$, how do I get it in this kind of equation? Is there any special trick to solve these type of integrals?
thanks in advance.
I was trying to derive the stefan-boltzman law from the planc's formula, I kind of got stuck with an integral
$$ \int_{0}^{\infty} \frac{x^3}{e^x -1} dx $$
I tried simplifying it with
$$ \int_{0}^{\infty} x^3 e^{-x} \sum_{n=0}^{\infty} e^{-nx} dx $$
Now I don't know what to do with the summation. I could evaluate
$$ \int_{0}^{\infty} x^3 e^{-x} dx = 6$$
pleas help me to get the rest of it, I see the answer comes with $\pi$, how do I get it in this kind of equation? Is there any special trick to solve these type of integrals?
thanks in advance.