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Ta có x = 2018
=> x + 1 = 2019
\(x^5-2019.x^4+2019.x^3-2019.x^2+2019.x-2020\)
\(=x^5-\left(x+1\right).x^4+\left(x+1\right).x^3-\left(x+1\right).x^2+\left(x+1\right).x-2020\)
\(=x^5-x^5+x^4-x^4+x^3-x^3+x^2-x^2+x-2020\)
\(=x-2020\)
Thay x = 2018 vào biểu thức , ta được
\(2018-2020=-2\)
Vậy giá trị biểu thức là -2
Nhận xét : ( x + y - 3 )^2018 >=0 và 2018.(2x-4)^2020 >= 0
=> (x+y-3)^2018 + 2018.(2x-4)^2020 >=0
Dấu = xảy ra khi : x + y - 3 = 0 và 2x - 4 = 0 => x = 2 và y = 1
Thay vào bt S :
S = ( 2 - 1)^2019 + (2-1)^2019
= 1^2019 + 1^2019 = 2
Ta có :\(\frac{x+4}{2018}+\frac{x+3}{2019}=\frac{x+2}{2020}+\frac{x+1}{2021}\)
=> \(\left(\frac{x+4}{2018}+1\right)+\left(\frac{x+3}{2019}+1\right)=\left(\frac{x+2}{2020}+1\right)+\left(\frac{x+1}{2021}+1\right)\)
=> \(\frac{x+2022}{2018}+\frac{x+2022}{2019}=\frac{x+2022}{2020}+\frac{x+2022}{2021}\)
=> \(\frac{x+2022}{2018}+\frac{x+2022}{2019}-\frac{x+2022}{2020}-\frac{x+2022}{2021}=0\)
=> \(\left(x+2022\right)\left(\frac{1}{2018}+\frac{1}{2019}-\frac{1}{2020}-\frac{1}{2021}\right)=0\)
Vì \(\frac{1}{2018}+\frac{1}{2019}-\frac{1}{2020}-\frac{1}{2021}\ne0\)
=> x + 2022 = 0
=> x = -2022
Vậy x = -2022
\(\frac{x+4}{2018}+\frac{x+3}{2019}=\frac{x+2}{2020}+\frac{x+1}{2021}\)
\(\frac{x+4}{2018}+1+\frac{x+3}{2019}+1=\frac{x+2}{2020}+1+\frac{x+1}{2021}+1\)
\(\frac{x+4}{2018}+\frac{2018}{2018}+\frac{x+3}{2019}+\frac{2019}{2019}=\frac{x+2}{2020}+\frac{2020}{2020}+\frac{x+1}{2021}+\frac{2021}{2021}\)
\(\frac{x+2022}{2018}+\frac{x+2022}{2019}=\frac{x+2022}{2020}+\frac{x+2022}{2021}\)
\(\frac{x+2022}{2018}+\frac{x+2022}{2019}-\frac{x+2022}{2020}-\frac{x+2022}{2021}=0\)
\(\left(x+2022\right)\left(\frac{1}{2018}+\frac{1}{2019}-\frac{1}{2020}-\frac{1}{2021}\right)=0\)
\(x+2022=0\left(\frac{1}{2018}+\frac{1}{2019}-\frac{1}{2020}-\frac{1}{2021}\ne0\right)\)
\(x=0-2022\)
\(x=-2022\)
Ta có: \(\left|x-\frac{2018}{2019}\right|\ge0\)
Và: \(\left|x-\frac{2019}{2020}\right|\ge0\)
\(\Rightarrow\left|x-\frac{2018}{2019}\right|+\left|x-\frac{2019}{2020}\right|\ge0\)
\(\Rightarrow\left|x-\frac{2018}{2019}\right|+\left|x-\frac{2019}{2020}\right|=0\)
\(\Leftrightarrow\left|x-\frac{2018}{2019}\right|=\left|x-\frac{2019}{2020}\right|=0\left(Vônghiệm\right)\)
\(\left|x-\frac{2018}{2019}\right|+\left|x-\frac{2019}{2020}\right|=0\)
Ta có:
\(\left\{{}\begin{matrix}\left|x-\frac{2018}{2019}\right|\ge0\\\left|x-\frac{2019}{2020}\right|\ge0\end{matrix}\right.\forall x.\)
\(\Rightarrow\left|x-\frac{2018}{2019}\right|+\left|x-\frac{2019}{2020}\right|=0\)
\(\Rightarrow\left\{{}\begin{matrix}\left|x-\frac{2018}{2019}\right|=0\\\left|x-\frac{2019}{2020}\right|=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x-\frac{2018}{2019}=0\\x-\frac{2019}{2020}=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=\frac{2018}{2019}\\x=\frac{2019}{2020}\end{matrix}\right.\)
\(\Rightarrow\) Vô lí vì x không thể đồng thời nhận 2 giá trị khác nhau.
Vậy không tồn tại giá trị nào của x thỏa mãn yêu cầu đề bài.
Chúc bạn học tốt!
\(x=\frac{2019^{2020}+1}{2019^{2019}+1}>\frac{2019^{2020}+1+2018}{2019^{2019}+1+2018}=\frac{2019^{2020}+2019}{2019^{2019}+2019}=\frac{2019\left(2019^{2019}+1\right)}{2019\left(2019^{2018}+1\right)}=\frac{2019^{2019}+1}{2019^{2018}+1}\)(1)
\(y=\frac{2019^{2019}+2020}{2019^{2018}+2020}< \frac{2019^{2019}+2020-2019}{2019^{2018}+2020-2019}=\frac{2019^{2019}+1}{2019^{2018}+1}\left(2\right)\)
Từ (1) và (2) \(\Rightarrow x>y\)
