Rút gọn 1/30+1/42+1/56+1/72+‧‧‧‧‧‧+1/9900

0 bình luận về “Rút gọn 1/30+1/42+1/56+1/72+‧‧‧‧‧‧+1/9900”

1. Đáp án:

   `1/{30}+1/{42}+1/{56}+1/{72}+‧‧‧‧‧‧+1/{9900}`

   `=1/{5.6}+1/{6.7}+1/{7.8}+1/{8.9}+…+1/{99.100}`

   `=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-…+1/{99}-1/{100}`

   `=1/5-1/{100}`

   `=19/{100}`

    

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2. Đáp án:

   Ta có : 

   $\dfrac{1}{30}$  + $\dfrac{1}{42}$  + $\dfrac{1}{56}$  + …. + $\dfrac{1}{9900}$ 

   = $\dfrac{1}{5.6}$ + $\dfrac{1}{6.7}$ + $\dfrac{1}{7.8}$ + …. + $\dfrac{1}{99.100}$

   = $\dfrac{1}{5}$ – $\dfrac{1}{6}$ + $\dfrac{1}{6}$ – $\dfrac{1}{7}$ + …. + $\dfrac{1}{99}$ – $\dfrac{1}{100}$

   = $\dfrac{1}{5}$ – $\dfrac{1}{100}$

   = $\dfrac{19}{100}$

   Giải thích các bước giải:

    

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