Đặt \(d=\left(x+1,2021x+2020\right)\).
Suy ra
\(\hept{\begin{cases}x+1⋮d\\2021x+2020⋮d\end{cases}}\Rightarrow\hept{\begin{cases}2021x+2021⋮d\\2021x+2020⋮d\end{cases}}\Rightarrow\left(2021x+2021\right)-\left(2021x+2020\right)=1⋮d\)
suy ra \(d=1\).
Suy ra đpcm.