can the prime really not solve this integral?

[Han]

(02-27-2014 02:11 PM)Terje Vallestad Wrote:  

(02-27-2014 12:21 PM)parisse Wrote:  You get a numeric answer with:
int(x^3/(exp(x)-1),x,0,inf)
then shift-enter.
x^3/(exp(x)-1) does not have an antiderivative than you can express with elementary function (special functions required, polylogs here). There is probably a trick than can give you the exact answer (pi^4/15) for the definite integral, any idea? On a voyage 200, you don't get the exact value by the way.

Possibly a dumb question, but why is the result dependent on the Rad/Deg setting when solving this? If the calc is in Degrees the result (on my calculator) is 372.07.... Other integrals involving exp(x) (for instance int(exp(x^2),x,0,.5)) seems not to be influenced by the Deg/Rad setting. Am I missing something?

Cheers, Terje

Do you also have complex mode on? Since \( e^{i\theta} = cos\theta + i \sin \theta \) the angle mode would affect the result.