Đáp án:
\(\dfrac{-3}{20}\)
Giải thích các bước giải:
\(\dfrac{-1}{20}\) + \(\dfrac{-1}{30}\) + \(\dfrac{-1}{42}\) + \(\dfrac{-1}{56}\) + \(\dfrac{-1}{72}\) + \(\dfrac{-1}{90}\)
`=` \(\dfrac{-1}{4.5}\) +\(\dfrac{-1}{5.6}\) + \(\dfrac{-1}{6.7}\)+ \(\dfrac{-1}{7.8}\) + \(\dfrac{-1}{8.9}\) + \(\dfrac{-1}{9.10}\)
`=` \(\dfrac{-1}{4}\) `-` \(\dfrac{-1}{5}\)` `+` `\(\dfrac{-1}{5}\)` - `\(\dfrac{-1}{6}\) `+` \(\dfrac{-1}{6}\) `-` \(\dfrac{-1}{7}\) `+` \(\dfrac{-1}{7}\) `-` \(\dfrac{-1}{8}\) `+` \(\dfrac{-1}{8}\) `-` \(\dfrac{-1}{9}\) `+` \(\dfrac{-1}{9}\) `-` \(\dfrac{-1}{10}\)
`=` \(\dfrac{-1}{4}\) + `1/10`
`=` \(\dfrac{-5}{20}\) + `2/20`
`=` \(\dfrac{-3}{20}\)
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