3

(\(\frac{9}{2.3}\) + \(\frac{9}{3.4}\) + ... + \(\frac{9}{199.200}\)).\(x\) = \(\frac{2}{5}\)

9.(\(\frac{1}{2.3}\) + \(\frac{1}{3.4}\) + ... + \(\frac{1}{199.200}\)).\(x\) = \(\frac{2}{5}\)

9.(\(\frac{1}{2} - \frac{1}{3}\) + \(\frac{1}{3}\) - \(\frac{1}{4}\) + ... + \(\frac{1}{199}\) - \(\frac{1}{200}\)).\(x\) = \(\frac{2}{5}\)

9.(\(\frac{1}{2}\) - \(\frac{1}{200}\)).\(x\) = \(\frac{2}{5}\)

9.\(\frac{99}{200}\).\(x\) = \(\frac{2}{5}\)

\(\frac{891}{200}\).\(x\) = \(\frac{2}{5}\)

\(x\) = \(\frac{2}{5}\) : \(\frac{891}{200}\)

\(x\) = \(\frac{80}{891}\)

Vậy \(x = \frac{80}{891}\)

khoa học tự nhiên nhé

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