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\(\left(-2022\right)+\left(-250\right)+\left(275+2022\right)\)
\(=\left(-2022\right)-250+275+2022\)
\(=\left[\left(-2022\right)+2022\right]+\left(275-250\right)\)
\(=0+25=25\)
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
\(\dfrac{-3}{7}\)(\(\dfrac{5}{9}\)+\(\dfrac{4}{9}\)) + 0
=\(\dfrac{-3}{7}\)
*Lần sau bạn viết rõ đề ra, để thế này nhiều ng sẽ không hiểu!
\(\dfrac{-3}{7}.\dfrac{5}{9}+\dfrac{4}{9}.\dfrac{-3}{7}+\left(2022\right)^0\)
\(=\dfrac{-3}{7}.\left(\dfrac{5}{9}+\dfrac{4}{9}\right)+1\)
\(=\dfrac{-3}{7}.1+1\)
\(=\dfrac{-3}{7}+1\)
\(=\dfrac{-3+7}{7}\)
\(=\dfrac{4}{7}\)
\(S=1+3^2+3^4+...+3^{2022}\)
\(3^2S=9S=3^2+3^4+3^6+...+3^{2024}\)
\(S=\dfrac{9S-S}{8}=\left(3^{2024}-1\right):8\)
d, không đáp án nào đúng
Lời giải:
$S=1+3^2+3^4+....+3^{2022}$
$9S=3^2S=3^2+3^4+3^6+...+3^{2024}$
$\Rightarrow 9S-S=3^{2024}-1$
$\Rightarrow S=\frac{3^{2024}-1}{8}$
Đáp án D.
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