Răspuns:
b=2019/2020
Explicație pas cu pas:
a=1/2020
b=1/1×2+1/2×3+...+1/2019×2020=
=1/1-1/2+1/2-1/3+....+1/2019-1/2020
=1/1-1/2020
=(2020-1)/2020
=2019/2020
