Răspuns:
Explicație pas cu pas:
1/2+1/6+1/12+................+1/a(a+1)=2021/2022
1/2=1/1-1/2
1/2·3=1/2-1/3
1/3·4=1/3-1/4
1/a(a+1)=1/a-1/(a+1)
..................................
Suma=1-1/(a+1)=(a+1-1)/(a+1)=a/(a+1)
a/(a+1)=2021/2022 ⇒ 2022a=2021(a+1)
2022a=2021a+2021 ⇒a=2021 ⇒raspuns: b
