Tính: B = 1/3.4 – 1/4.5 – 1/5.6 – 1/6.7 – 1/7.8 – 1/8.9 – 1/9.10

Tính: B = 1/3.4 – 1/4.5 – 1/5.6 – 1/6.7 – 1/7.8 – 1/8.9 – 1/9.10

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  1. Đáp án:

    `B=`$\frac{1}{3.4}$ – $\frac{1}{4.5}$ -…-$\frac{1}{9.10}$ 

    `B=“1/3`-`1/4`+`1/4`-`1/5`+…+`1/9`-`1/10`

    `B=“1/3` -`1/4`-`1/4`+ `1/10`

    `B=` `-1/15`

     

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  2. $B = \dfrac{1}{3.4} – \dfrac{1}{4.5} – \dfrac{1}{5.6} – \dfrac{1}{6.7} – \dfrac{1}{7.8} – \dfrac{1}{8.9} – \dfrac{1}{9.10}$ 

    $B = \dfrac{1}{3} – \dfrac{1}{4} – (\dfrac{1}{4} – \dfrac{1}{5}) – (\dfrac{1}{5} – \dfrac{1}{6}) – (\dfrac{1}{6} – \dfrac{1}{7}) – (\dfrac{1}{7} – \dfrac{1}{8}) – (\dfrac{1}{8} – \dfrac{1}{9}) – (\dfrac{1}{9} – \dfrac{1}{10})$ 

    $B = \dfrac{1}{3} – \dfrac{1}{4} – \dfrac{1}{4} + \dfrac{1}{10} = -\dfrac{1}{15}$

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