So sánh 2021³ và 2020.2021.2022. 

Xét A = 2021³ = 2021.2021.2021

Suy ra: $\frac{A}{2021}=2021.2021$

Xét B = 2020.2021.2022

Suy ra: $\frac{B}{2021}=2020.2022$

$\frac{B}{2021}=2021.2022-2022=2021.\left(2021+1\right)-2021-1=2021.2021-1<2021.2021$

Hay $\frac{B}{2021}<\frac{A}{2021}$

Vậy A > B hay 2021³ > 2020.2021.2022