Đặt ƯCLN (n+2019; n+2020)=d
\(\Rightarrow\left\{{}\begin{matrix}\left(n+2020\right)⋮d\\\left(n+2019\right)⋮d\end{matrix}\right.\Rightarrow\left(n+2020\right)-\left(n+2019\right)⋮d\Rightarrow1⋮d\Rightarrow d=1\)
⇒ƯCLN (n+2019; n+2020)=d=1
\(\Rightarrow\frac{n+2019}{n+2020}\)là phân số tối giản (đpcm)
Gọi dϵƯC(n+2019,n+2020)với d ∈N*
⇒n+2019⋮d,n+2020⋮
⇒(n+2020)-(n+2019)=1⋮d⇒d =1
⇒ĐPCM