x-1:10-1:15-1:21-...-1:120=7:8
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=>x-(2/20+2/30+...+2/240)=3/8
=>x-2(1/4-1/5+1/5-1/6+...+1/15-1/16)=3/8
=>x-2*3/16=3/8
=>x=3/8+3/8=3/4
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{x}{2008}-\frac{1}{10}-\frac{1}{15}-\frac{1}{21}-...-\frac{1}{120}=\frac{5}{8}\)
\(\Rightarrow\frac{x}{2008}-[2\left(\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+...+\frac{1}{240}\right)]=\frac{5}{8}\)
\(\Rightarrow\frac{x}{2008}-[2\left(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{15.16}\right)]=\frac{5}{8}\)
\(\Rightarrow\frac{x}{2008}-[2\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{5}-\frac{1}{16}\right)]=\frac{5}{8}\)
\(\Rightarrow\frac{x}{2008}-[2.\frac{3}{16}]=\frac{5}{8}\)
\(\Rightarrow\frac{x}{2008}=1\)
\(\Rightarrow x=2008\)
\(\frac{7}{x}+\frac{4}{5.9}+\frac{4}{9.13}+\frac{4}{13.17}+...+\frac{4}{41.45}=\frac{29}{45}\)
\(\Rightarrow\frac{7}{x}+\left(\frac{4}{5.9}+\frac{4}{9.13}+\frac{4}{13.17}+...+\frac{4}{41.45}\right)=\frac{29}{45}\)
\(\Rightarrow\frac{7}{x}+\left(\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+...+\frac{1}{41}-\frac{1}{45}\right)=\frac{29}{45}\)
\(\Rightarrow\frac{7}{x}+\left(\frac{1}{5}-\frac{1}{45}\right)=\frac{29}{45}\)
\(\Rightarrow\frac{7}{x}+\frac{8}{45}=\frac{29}{45}\)
\(\Rightarrow\frac{7}{x}=\frac{21}{45}\)
\(\Rightarrow x=15\)
![](https://rs.olm.vn/images/avt/0.png?1311)
hãy k nếu muốn
và nếu muốn thì hãy k mik bất cứ lúc nào
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{x}{2008}-\left(\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+...+\frac{1}{120}\right)=\frac{5}{8}\)
\(\frac{x}{2008}-\frac{3}{8}=\frac{5}{8}\)
\(\frac{x}{2008}=1\)
x=2008
![](https://rs.olm.vn/images/avt/0.png?1311)
bạn gửi câu trả lời của bạn trước nhé rồi mình sẽ gửi câu trả lời cho
\(\frac{7}{8}=x-\frac{1}{10}-\frac{1}{15}-\frac{1}{21}-...-\frac{1}{120}\)
\(\frac{7}{4}=2x-\left(\frac{2}{20}+\frac{2}{30}+\frac{2}{42}+...+\frac{2}{240}\right)\)
\(\frac{7}{4}=2x-2\left(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{15.16}\right)\)
\(\frac{7}{4}=2x-2\left(\frac{1}{4}-\frac{1}{16}\right)\)
\(\frac{7}{4}=2x-\frac{3}{8}\)
\(2x=\frac{17}{8}\)
\(x=\frac{17}{16}\)
Vậy \(x=\frac{17}{16}\)