Question Number 26568 by abdo imad last updated on 26/Dec/17
$${let}\:{give}\:\xi\left({x}\right)=\:\sum_{{n}=\mathrm{1}} ^{\propto} \frac{\mathrm{1}}{{n}^{{x}} }\:\:{prove}\:{that}\:\xi\left({x}\right)−_{{x}−>\propto} \mathrm{1}\sim\mathrm{2}^{−{x}} \\ $$