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\(5^{3x}:5^5=5^{2020}:5^{2016}\)
\(5^{3x-5}=5^{2020-2016}=5^4\)
\(3x-5=4\Leftrightarrow3x=4+5=9\Leftrightarrow x=9:3=3\)
\(\frac{5^{3x}}{5^5}=\frac{5^{2020}}{5^{2016}}=5^{2020-2016}=5^4\Rightarrow5^{3x}=5^4.5^5=5^{4+5}=5^9\Rightarrow x=3\)
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1. \(\dfrac{2019}{2020}-\left(\dfrac{2019}{2020}-\dfrac{2020}{2021}\right)\)
\(=\dfrac{2019}{2020}-\dfrac{2019}{2020}+\dfrac{2020}{2021}\)
\(=0+\dfrac{2020}{2021}=\dfrac{2020}{2021}\)
Giải:
1) \(\dfrac{2019}{2020}-\left(\dfrac{2019}{2020}-\dfrac{2020}{2021}\right)\)
\(=\dfrac{2019}{2020}-\dfrac{2019}{2020}+\dfrac{2020}{2021}\)
\(=\left(\dfrac{2019}{2020}-\dfrac{2019}{2020}\right)+\dfrac{2020}{2021}\)
\(=0+\dfrac{2020}{2021}\)
\(=\dfrac{2020}{2021}\)
2) \(\dfrac{2}{9}+\dfrac{7}{9}:\left(\dfrac{42}{5}-\dfrac{7}{5}\right)\)
\(=\dfrac{2}{9}+\dfrac{7}{9}:7\)
\(=\dfrac{2}{9}+\dfrac{1}{9}\)
\(=\dfrac{1}{3}\)
3) \(\dfrac{3}{4}+\dfrac{x}{4}=\dfrac{5}{8}\)
\(\dfrac{x}{4}=\dfrac{5}{8}-\dfrac{3}{4}\)
\(\dfrac{x}{4}=\dfrac{-1}{8}\)
\(\Rightarrow x=\dfrac{4.-1}{8}=\dfrac{-1}{2}\)
4) \(\left|3x+1\right|-\dfrac{1}{4}=\dfrac{-1}{4}\)
\(\left|3x-1\right|=\dfrac{-1}{4}+\dfrac{1}{4}\)
\(\left|3x-1\right|=0\)
\(3x-1=0\)
\(3x=0+1\)
\(3x=1\)
\(x=1:3\)
\(x=\dfrac{1}{3}\)
Chúc bạn học tốt!
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A=7 mu 2020 mu 2019-3 mu 2016 mu 2015 :5 chung to A la so chan
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Bài 3:
Gọi số học sinh là x
Theo đề, ta có: \(x-2\in BC\left(3;4;6\right)\)
mà 35<x<40
nên x-2=36
hay x=38
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a: =>7x+39=25
=>7x=-14
=>x=-2
b: =>5^3x+7=5^2018(5^2-1)
=>5^3x+7=5^2018*24(loại)
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S=(1-2-3+4)+(5-6-7+8)+........+(2013-2014-2015+2016)+(2017-2018-2019+2020)
=0+0+0+.......+0+0=0
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