Question Number 181733 by SANOGO last updated on 30/Nov/22
$$\left.\mathrm{1}\right){calcul}\:{n}−+{oo}:\:{sn}=\underset{{k}={n}+\mathrm{1}} {\overset{\mathrm{2}{n}} {\sum}}\:\frac{\mathrm{1}}{{k}} \\ $$$$\left.\mathrm{2}\right){find}:\:\underset{{k}=\mathrm{1}} {\overset{+{oo}} {\sum}}\:\frac{\left(−\mathrm{1}\right)^{{k}+\mathrm{1}} }{{k}} \\ $$