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2 tháng 5 2020
a) \(\left(\frac{3x}{7}+1\right):\left(-4\right)=\frac{-1}{28}\)
\(\Rightarrow\frac{3}{7}.x+1=\frac{-1}{28}.\left(-4\right)\)
\(\Rightarrow\frac{3}{7}.x=\frac{1}{7}-1\)
\(\Rightarrow\frac{3}{7}.x=\frac{-6}{7}\)
\(\Rightarrow x=\frac{-6}{7}:\frac{3}{7}\)
\(\Rightarrow x=\frac{-6}{7}.\frac{7}{3}\)
\(\Rightarrow x=-2\)
b) x+30%x=-1.3 mình coi 1.3 là 1,3 nhé !
\(\Rightarrow x\left(30\%+1\right)=-1,3\)
\(\Rightarrow x\left(\frac{13}{10}\right)=-\frac{13}{10}\)
\(\Rightarrow x=-\frac{13}{10}:\frac{13}{10}\)
\(\Rightarrow x=-1\)
15 tháng 5 2017
\(\frac{1}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{x}-\frac{1}{x+2}\right)=\frac{5}{11}.\)
\(\frac{1}{2}\left(1-\frac{1}{x+2}\right)=\frac{5}{11}\)
\(1-\frac{1}{x+2}=\frac{5}{11}:\frac{1}{2}\)
\(1-\frac{1}{x+2}=\frac{5}{11}\cdot2=\frac{10}{11}\)
\(\frac{1}{x+2}=1-\frac{10}{11}\)
\(\frac{1}{x+2}=\frac{1}{11}\)
\(\Rightarrow x+2=11\)
\(\Rightarrow x=11-2=9\)
vậy x=9
ko viết đề bài nha
4 tháng 7 2019
\(G=\frac{2^2}{1.3}.\frac{3^2}{2.4}....\frac{19^2}{18.20}\)
\(=\frac{2.2}{1.3}.\frac{3.3}{2.4}......\frac{19.19}{18.20}\)
\(=\frac{2.3....19}{1.2...18}.\frac{2.3...19}{3.4....20}\)
\(=\frac{19}{1}.\frac{1}{20}\)
\(=\frac{19}{20}\)
9 tháng 5 2019
\(\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+\frac{1}{5\cdot7}+...+\frac{1}{x(x+2)}=\frac{20}{41}\)
\(\Rightarrow\frac{1}{2}\left[\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+...+\frac{2}{x(x+2)}\right]=\frac{20}{41}\)
\(\Rightarrow\frac{1}{2}\left[1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+2}\right]=\frac{20}{41}\)
\(\Rightarrow\frac{1}{2}\left[1-\frac{1}{x+2}\right]=\frac{20}{41}\)
\(\Rightarrow1-\frac{1}{x+2}=\frac{20}{41}:\frac{1}{2}\)
\(\Rightarrow1-\frac{1}{x+2}=\frac{40}{41}\)
\(\Rightarrow\frac{1}{x+2}=1-\frac{40}{41}\)
\(\Rightarrow\frac{1}{x+2}=\frac{1}{41}\Leftrightarrow x+2=41\Leftrightarrow x=39\)
9 tháng 5 2019
\(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+2}=\frac{20}{41}.\)
\(1-\frac{1}{x+2}=\frac{20}{41}\Rightarrow\frac{1}{x+2}=\frac{21}{41}=\frac{21}{21x+42}\Rightarrow21x+42=41\Rightarrow x=-\frac{1}{21}\)
C
5 tháng 5 2017
\(\left(\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{97.99}\right)-x=-\dfrac{100}{99}\)
\(\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{99}\right)-x=-\dfrac{100}{99}\)
\(\left(1-\dfrac{1}{99}\right)-x=-\dfrac{100}{99}\)
\(\dfrac{98}{99}-x=-\dfrac{100}{99}\)
\(x=\dfrac{98}{99}-\left(-\dfrac{100}{99}\right)\)
\(x=\dfrac{198}{99}\)
Vậy \(x=\dfrac{198}{99}\)
15 tháng 8 2018
\(\left(1+\frac{1}{1\cdot3}\right)\left(1+\frac{1}{2\cdot4}\right)\left(1+\frac{1}{3\cdot5}\right)+...+\left(1+\frac{1}{2014\cdot2016}\right)=\frac{x}{1008}\)
\(\Rightarrow\frac{4}{3}\cdot\frac{9}{8}\cdot\frac{16}{15}\cdot...\cdot\frac{4060225}{4060224}=\frac{x}{1008}\)
\(\Rightarrow\frac{\left(2\cdot2\right)\left(3\cdot3\right)\left(4\cdot4\right)...\left(2015\cdot2015\right)}{\left(1\cdot3\right)\left(2\cdot4\right)\left(3\cdot5\right)...\left(2014\cdot2016\right)}=\frac{x}{1008}\)
\(\Rightarrow\frac{\left(2\cdot3\cdot4\cdot...\cdot2015\right)\left(2\cdot3\cdot4\cdot...\cdot2015\right)}{\left(1\cdot2\cdot3\cdot...\cdot2014\right)\left(3\cdot4\cdot5\cdot...\cdot2016\right)}=\frac{x}{1008}\)
\(\Rightarrow\frac{2015\cdot2}{1\cdot2016}=\frac{x}{1008}\)
\(\Rightarrow\frac{2015}{1008}=\frac{x}{1008}\)
\(\Rightarrow x=2015\)
CT
\(\frac{\text{4}5-x}{1963}+\frac{\text{4}0-x}{1968}+\frac{35-x}{1973}+\frac{30-x}{1978}+\text{4}=0\)
4
11 tháng 1 2020
tham khảo nhé
https://olm.vn/hoi-dap/detail/103171879928.html
C
11 tháng 1 2020
\(\frac{45-x}{1963}+\frac{40-x}{1968}+\frac{35-x}{1973}+\frac{30-x}{1978}+4=0\)
\(\Leftrightarrow\left(\frac{45-x}{1963}+1\right)+\left(\frac{40-x}{1968}+1\right)+\left(\frac{35-x}{1973}+1\right)+\left(\frac{30-x}{1978}+1\right)=0\)
\(\Leftrightarrow\frac{2008-x}{1963}+\frac{2008-x}{1968}+\frac{2008-x}{1973}+\frac{2008-x}{1973}=0\)
\(\Leftrightarrow\left(2008-x\right)\left(\frac{1}{1963}+\frac{1}{1968}+\frac{1}{1973}+\frac{1}{1978}\right)=0\)
\(\Leftrightarrow x=2008\)
TT
2
20 tháng 8 2016
\(\Leftrightarrow\frac{1}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{47}-\frac{1}{49}\right)=\frac{1}{x}\)
\(\Leftrightarrow\frac{1}{2}\left(1-\frac{1}{49}\right)=\frac{1}{x}\Rightarrow x=\frac{49}{24}\)
20 tháng 8 2016
\(\frac{1}{2}.\left(1-\frac{1}{3}\right)+\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}\right)+\frac{1}{2}.\left(\frac{1}{5}-\frac{1}{7}\right)+...+\frac{1}{2}.\left(\frac{1}{47}-\frac{1}{49}\right)=\frac{1}{x}\)
\(\frac{1}{2}.\left(1-\frac{1}{49}\right)=\frac{1}{x}\)
\(\frac{24}{49}=\frac{1}{x}\)\(\Rightarrow x=\frac{49}{24}\)
-\(x\) + 30% \(\times\) \(x\) = -1,3
-\(x\) + 0,3\(\times\) \(x\) = -1,3
\(x\times\) ( 1 - 0,3) = -1,3
\(x\) \(\times\)(- 0,7) = -1,3
\(x\) = (-1,3) : (-0,7)
\(x\) = \(\dfrac{13}{7}\)