Question Number 30435 by abdo imad last updated on 22/Feb/18
$${let}\:\:{f}_{{n}} \left({x}\right)=\:\:\sum_{{n}=\mathrm{0}} ^{\infty} \:{e}^{−{nx}} \:\:{calculate}\:\:\int_{\mathrm{1}} ^{{e}} \:{f}_{{n}} \left({x}\right){dx}. \\ $$
let-f-n-x-n-0-e-nx-calculate-1-e-f-n-x-dx-