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2018 A = 2018 - 2018^2 + 2018^3 +...- 2018^2018 + 2018^2019
=> A + 2018 A = 1 +2018^2019
=> 2019 A = 1 + 2018^2019
=> 2019 A - 1 = 2018^2019
=> 2019 A -1 là 1 lũy thừa của 2018
A=(1+2018)+2018^2(1+2018)+...+2018^2016(1+2018)
=2019(1+2018^2+...+2018^2016) chia hết cho 2019
=>A chia 2019 dư 0
\(M=\left(2018+2018^2\right)+\left(2018^3+2018^4\right)+...+\left(2018^{2017}+2018^{2018}\right)\)
\(=2018\left(1+2018\right)+2018^3\left(1+2018\right)+...+2018^{2017}\left(1+2018\right)\)
\(=2018.2019+2018^3.2019+...+2018^{2017}.2019\)
\(=2019\left(2018+2018^3+...+2018^{2017}\right)⋮2019\)
b/ \(M=2018+2018^2+...+2018^{2018}\)
\(2018M=2018^2+2018^3+...+2018^{2018}+2018^{2019}\)
Lấy dưới trừ trên:
\(2018M-M=-2018+2018^{2019}\)
\(\Rightarrow2017M=2018^{2019}-2018\)
\(\Rightarrow M=\frac{2018^{2019}-2018}{2017}=\frac{2018^{2019}}{2017}-\frac{2017+1}{2017}=\frac{2018^{2019}}{2017}-1-\frac{1}{2017}\)
\(\Rightarrow M=N-\frac{1}{2017}\Rightarrow M< N\)
Ta có:
1+2018+20182+20183+...+20187
= (1+2018)+(20182+20183)+(20184+20185)+(20186+20187)
= (1+2018)+20182 (1+2018) +20184 (1+2018)+20186 (1+2018)
= (1+2018) ( 1+20182+20184+20186)
= 2019 ( 1+20182+20184+20186) chia hết cho 9 (đpcm)
Học tốt
Hand@