Question Number 121041 by bramlexs22 last updated on 05/Nov/20
$$\:\sum_{\mathrm{k}=\mathrm{1}} ^{\mathrm{n}} \:\left(−\mathrm{1}\right)^{\mathrm{k}} .\mathrm{k}\:=?\: \\ $$
Answered by Dwaipayan Shikari last updated on 05/Nov/20
$$−\mathrm{1}+\mathrm{2}−\mathrm{3}+\mathrm{4}−\mathrm{5}+\mathrm{6}−\mathrm{7}+\mathrm{8}−…=\frac{{n}}{\mathrm{2}} \\ $$