Răspuns:
Explicație pas cu pas:
[2021-(1/2+2/3+3/4+...+2020/2021)-(1/2+1/3+1/4+...+1/2021)]=
[2021-[(1/2+2/3+3/4+...+2020/2021)+(1/2+1/3+1/4+...+1/2021)]=
In fiecare parantza rotunda ai 2020 termeni , pe care-i grupezi 2 cate 2
[2021-[(1/2+1/2)+(2/3+1/3)+(3/4+1/4)+....(2020/2021+1/2021)]=
Parantezele rotunde sunt ega;le cu 1=>
(2021-1-1-1-...-1(de 1010 0ri))=
2021-1010=1011
