Triple exponential integral
We show the proof of the following integral: ∫π0eecosxcossinxcos(ecosxsinsinx)dx=πe
On the way we will find this beautiful result:
∫π0eeeix+eee−ixdx=2πe
Proof
∫π0eecosxcossinxcos(ecosxsinsinx)dx=∫π0eecosxcossinx[eiecosxsinsinx+e−iecosxsinsinx2]dx=12∫π0eecosxcossinx+iecosxsinsinx+eecosxcossinx−iecosxsinsinxdx=12∫π0eecosx(cossinx+isinsinx)+eecosx(cossinx−isinsinx)dx=12∫π0eecosxeisinx+eecosxe−isinxdx=12∫π0eecosx+isinx+eecosx−isinxdx=12∫π0eeeix+eee−ixdx=12∫π0[∞∑n=0(eeix)nn!+∞∑0(ee−ix)nn!]dx=12∫π0∞∑n=0(eeix)n+(ee−ix)nn!dx=12∞∑n=01n!∫π0(eeix)n+(ee−ix)ndx=12∞∑n=01n![∫π0(eeix)ndx+∫π0(ee−ix)ndx]=12∞∑n=01n![∫π0(eeix)ndx−∫0π(ee−ix)ndx]=12∞∑n=01n![∫π0(eeix)ndx+∫0−π(eeix)ndx]=12∞∑n=01n!∫π−π(eeix)ndx=12∞∑n=01n!∮γeznzidz(where γ(x)=eixx∈[−π,π])=12∞∑n=01n!2π(Cauchy integral formula)=πe
∫π0eecosxcossinxcos(ecosxsinsinx)dx=πe
Corollary
∫π0eeeix+eee−ixdx=2πe
No comments:
Post a Comment