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ln-1-e-u-du-




Question Number 93553 by Ar Brandon last updated on 13/May/20
∫ln(1+e^u )du
$$\int{ln}\left(\mathrm{1}+\mathrm{e}^{\mathrm{u}} \right)\mathrm{du} \\ $$
Commented by Tony Lin last updated on 13/May/20
let −e^u =z  dz=zdu  ∫  ((ln(1−z))/z)dz  =−Li_2 (z)+c  =−Li_2 (−e^u )+c  Li_2 (z)=Σ_(k=1) ^∞ (z^k /k^2 )
$${let}\:−{e}^{{u}} ={z}\:\:{dz}={zdu} \\ $$$$\int\:\:\frac{{ln}\left(\mathrm{1}−{z}\right)}{{z}}{dz} \\ $$$$=−{Li}_{\mathrm{2}} \left({z}\right)+{c} \\ $$$$=−{Li}_{\mathrm{2}} \left(−{e}^{{u}} \right)+{c} \\ $$$${Li}_{\mathrm{2}} \left({z}\right)=\underset{{k}=\mathrm{1}} {\overset{\infty} {\sum}}\frac{{z}^{{k}} }{{k}^{\mathrm{2}} } \\ $$
Commented by Ar Brandon last updated on 13/May/20
Okay thanks ��

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