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-2/3 + 3/7.x = 19/21
3/7.x = 19/21 - -2/3 ( 19 phần 21 - âm 2 phần 3)
3/7.x = 11/7
x = 11/7 : 3/7
x = 11/3
tk mjk nha
Ta có:
\(\frac{2}{7}S=\frac{2}{7}.\left(\frac{7}{3.5}+\frac{7}{5.7}+...+\frac{7}{2015.2017}\right)\)
\(\Rightarrow\frac{2}{7}S=\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+....+\frac{2}{2015.2017}\)
\(\Rightarrow\frac{2}{7}S=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2015}-\frac{1}{2017}\)
\(\Rightarrow\frac{2}{7}S=\frac{1}{3}-\frac{1}{2017}=\frac{2014}{6051}\)
\(\Rightarrow S=\frac{2014}{6051}:\frac{2}{7}=1\frac{998}{6051}\)
S = \(\frac{7}{3.5}+\frac{7}{5.7}+\frac{7}{7.9}+....+\frac{7}{2015.2017}\)
2S = \(7\).( \(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+....+\frac{2}{2015.2017}\))
2S = \(7.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+....+\frac{1}{2015}-\frac{1}{2017}\right)\)
2S = \(7.\left(\frac{1}{2}-\frac{1}{2017}\right)\)
\(2S=7.\frac{2015}{4034}\)
\(S=\frac{7.2015}{4034.2}=1,74826475\)
1)x=-30
2)x=-81
3)x=4
4)x=62
5)x=6
6)-13
7)-13
8)-31
9)x=-6;0;6;12
tk minh nha
\(2\frac{1}{6}+x:\frac{6}{7}=-75\%\)
\(\frac{13}{6}+x:\frac{6}{7}=-\frac{3}{4}\)
\(x:\frac{6}{7}=-\frac{3}{4}-\frac{13}{6}=-\frac{35}{12}\)
\(x=-\frac{35}{12}x\frac{6}{7}=\frac{5}{2}\)
vậy \(x=\frac{5}{2}\)
\(2\frac{1}{6}+x\div\frac{6}{7}\)\(=-75\%\)
\(\frac{13}{6}+x\div\frac{6}{7}\)\(=-0,75\)
\(\frac{13}{6}+x\div\frac{6}{7}\) \(=-0,75\)
\(\frac{13}{6}+x\) \(=-0,75\times\frac{6}{7}\)
\(\frac{13}{6}+x\) \(=\frac{-9}{14}\)
\(x\) \(=\frac{-9}{14}-\frac{13}{6}\)
\(x\) \(=\frac{-59}{21}\)
Tk cho mk nhé!