cho mk cảm ơn bạn giải ra hộ mk nha !
\(\)\(x×\frac{2}{5}=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}\)
\(x×\frac{2}{5}=\frac{4}{25}\)
\(x=\frac{4}{25}:\frac{2}{5}\)
\(x=\frac{2}{5}\)
vậy \(x=\frac{2}{5}\)
nhầm
\(x×\frac{2}{25}=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}\)
\(x×\frac{2}{25}=\frac{4}{25}\)
\(x=\frac{4}{25}:\frac{2}{25}\)
\(x=2\)
vậy \(x=2\)
\(x\times\frac{2}{25}=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}\)
Ta có : \(A=\frac{1}{7}+\frac{1}{91}+\frac{1}{247}+\frac{1}{475}=\frac{1}{1\cdot7}+\frac{1}{7\cdot13}+\frac{1}{13\cdot19}+\frac{1}{19\cdot25}\)
\(=\frac{1}{6}\left(\frac{6}{1\cdot7}+\frac{6}{7\cdot13}+\frac{6}{13\cdot19}+\frac{6}{19\cdot25}\right)\)
\(=\frac{1}{6}\left(1-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+...+\frac{1}{19}-\frac{1}{25}\right)\)
\(=\frac{1}{6}\left(1-\frac{1}{25}\right)=\frac{1}{6}\cdot\frac{24}{25}=\frac{1}{1}\cdot\frac{4}{25}=\frac{4}{25}\)
=> \(x\times\frac{2}{25}=A\)
=> \(x\times\frac{2}{25}=\frac{4}{25}\)
=> \(x=\frac{4}{25}:\frac{2}{25}=\frac{4}{25}\cdot\frac{25}{2}=2\)
