k=(1/2023-1)(1/2022-1)(1/2021-1)...(1/2-1)
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B = \(\dfrac{1}{2002}\) + \(\dfrac{2}{2021}\) + \(\dfrac{3}{2020}\)+...+ \(\dfrac{2021}{2}\) + \(\dfrac{2022}{1}\)
B = \(\dfrac{1}{2002}\) + \(\dfrac{2}{2021}\) + \(\dfrac{3}{2020}\)+...+ \(\dfrac{2021}{2}\) + 2022
B = 1 + ( 1 + \(\dfrac{1}{2022}\)) + ( 1 + \(\dfrac{2}{2021}\)) + \(\left(1+\dfrac{3}{2020}\right)\)+ ... + \(\left(1+\dfrac{2021}{2}\right)\)
B = \(\dfrac{2023}{2023}\) + \(\dfrac{2023}{2022}\) + \(\dfrac{2023}{2021}\) + \(\dfrac{2023}{2020}\) + ...+ \(\dfrac{2023}{2}\)
B = 2023 \(\times\) ( \(\dfrac{1}{2023}\) + \(\dfrac{1}{2022}\) + \(\dfrac{1}{2021}\) + \(\dfrac{1}{2020}\)+ ... + \(\dfrac{1}{2}\))
Vậy B > C
A = \(\dfrac{1}{2021.2022}\) + \(\dfrac{1}{2022.2023}\) + \(\dfrac{1}{2023.2024}\) + \(\dfrac{1}{2024.2025}\) - \(\dfrac{4}{2021.2025}\)
A = \(\dfrac{1}{2021}\) - \(\dfrac{1}{2022}\) + \(\dfrac{1}{2022}\) - \(\dfrac{1}{2023}\) + \(\dfrac{1}{2023}\) - \(\dfrac{1}{2024}\) + \(\dfrac{1}{2024}\) - \(\dfrac{1}{2025}\) - \(\dfrac{1}{2021}\) + \(\dfrac{1}{2025}\)
A = (\(\dfrac{1}{2021}\) - \(\dfrac{1}{2021}\)) + (\(\dfrac{1}{2022}\) - \(\dfrac{1}{2022}\)) + (\(\dfrac{1}{2023}\) - \(\dfrac{1}{2023}\)) + (\(\dfrac{1}{2024}\) - \(\dfrac{1}{2024}\)) + (\(\dfrac{1}{2025}\) - \(\dfrac{1}{2025}\))
A = 0 + 0 +0 + 0+ ... + 0
A = 0
a: \(98^{10}\cdot A=\dfrac{98^{98}+98^{10}}{98^{98}+1}=1+\dfrac{98^{10}-1}{98^{98}+1}\)
\(98^{10}\cdot B=\dfrac{98^{99}+98^{10}}{98^{99}+1}=1+\dfrac{98^{10}-1}{98^{99}+1}\)
98^88+1>98^99+1
=>A<B
b: \(\dfrac{1}{2022^2}\cdot C=\dfrac{2022^{2023}+1}{2022^{2023}+2022^2}=1+\dfrac{1-2022^2}{2022^{2023}+2022^2}\)
\(\dfrac{1}{2022^2}\cdot D=\dfrac{2022^{2021}+1}{2022^{2021}+2022^2}=1+\dfrac{1-2022^2}{2022^{2021}+2022^2}\)
2022^2023>2022^2021
=>2022^2023+2022^2>2022^2021+2022^2
=>\(\dfrac{2022^2-1}{2022^{2023}+2022^2}< \dfrac{2022^2-1}{2022^{2021}+2022^2}\)
=>\(\dfrac{1-2022^2}{2022^{2023}+2022^2}>\dfrac{1-2022^2}{2022^{2021}+2022^2}\)
=>C>D
\(=\left(\dfrac{15}{2021}+\dfrac{16}{2022}-\dfrac{115}{2023}\right)\cdot\dfrac{3-2-1}{6}=0\)
\(\left(\dfrac{15}{2021}+\dfrac{16}{2022}-\dfrac{115}{2023}\right)\cdot\left(\dfrac{1}{2}-\dfrac{1}{3}-\dfrac{1}{6}\right)=\left(\dfrac{15}{2021}+\dfrac{8}{1011}-\dfrac{115}{2023}\right)\cdot\left(\dfrac{3}{6}-\dfrac{2}{6}-\dfrac{1}{6}\right)=\left(\dfrac{15}{2021}+\dfrac{8}{1011}-\dfrac{115}{2023}\right)\cdot0=0\)
\(M=\dfrac{10^{2021}+1}{10^{2022}+1}\)
\(N=\dfrac{10^{2022}+1}{10^{2023}+1}< \dfrac{10^{2022}+1+9}{10^{2023}+1+9}=\dfrac{10^{2022}+10}{10^{2023}+10}=\dfrac{10\left(10^{2021}+1\right)}{10\left(10^{2022}+1\right)}\)
\(=\dfrac{10^{2021}+1}{10^{2022}+1}=M\)
Vậy \(M>N\)
K = (\(\dfrac{1}{2023}\) - 1)(\(\dfrac{1}{2022}\) -1)(\(\dfrac{1}{2021}\) - 1)...(\(\dfrac{1}{2}\)-1)
K = \(\dfrac{1-2023}{2023}\).\(\dfrac{1-2022}{2022}\).\(\dfrac{1-2021}{2021}\)....\(\dfrac{1-2}{2}\)
K = \(\dfrac{-2022}{2023}\).\(\dfrac{\left(-2021\right)}{2022}\).\(\dfrac{\left(-2020\right)}{2021}\)....\(\dfrac{\left(-1\right)}{2}\)
Xét dãy số: 1; 2; 3; 4;...; 2022
Dãy số trên là dãy số cách đều với khoản cách là 2-1 = 1
Dãy số trên có số số hạng là: (2022 - 1): 1 + 1 = 2022
Vậy tử số của K là tích của 2022 số âm nên tử số là một số dương
K = \(\dfrac{2022.2021.2020...1}{2023.2022.2021.2020....2}\)
K = \(\dfrac{2022.2021.2020...2}{2022.2021.2020...2}\). \(\dfrac{1}{2023}\)
K = \(\dfrac{1}{2023}\)