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Đặt A = \(\frac{2019^{2019}+1}{2019^{2020}+1}\)
=> \(2019A=\frac{2019^{2020}+2019}{2019^{2020}+1}=1+\frac{2018}{2019^{2020}+1}\)
Đặt B = \(\frac{2019^{2020}+1}{2019^{2021}+1}\)
=> \(2019B=\frac{2019^{2021}+2019}{2019^{2021}+1}=1+\frac{2018}{2019^{2021}+1}\)
Vì \(\frac{2018}{2019^{2020}+1}>\frac{2018}{2019^{2021}+1}\Rightarrow1+\frac{2018}{2019^{2020}+1}>1+\frac{2018}{2019^{2021}+1}\Rightarrow10A>10B\Rightarrow A>B\)
c) \(M=\frac{2019}{2020}+\frac{2020}{2021}\) và \(N=\frac{2019+2020}{2020+2021}\)
Ta có \(\frac{2019}{2020}>\frac{2019}{2020+2021}\)
\(\frac{2020}{2021}>\frac{2020}{2020+2021}\)
\(\Rightarrow\frac{2019}{2020}+\frac{2020}{2021}< \frac{2019+2020}{2020+2021}=N\)
\(\Rightarrow M>N\)
Ta có : 2019^10+2019^9=2019^9.(2019+1)=2019^9.2020
Mà 2020^10>2019^9.2020
=>2020^10>2019^10+2019^9