Tính 1/1.3 +1/3.5 +1/5.7 +……. +1/2009.2011

0 bình luận về “Tính 1/1.3 +1/3.5 +1/5.7 +……. +1/2009.2011”

1. `1/1.3 +1/3.5 +1/5.7 +……. +1/2009.2011`

   ` = 1/2 . (2/1.3 +2/3.5 +2/5.7 +……. +2/2009.2011)`

   ` = 1/2 . (1 – 1/3 + 1/3 – 1/5 + 1/5 – 1/7 + …. + 1/2009 – 1/2011)`

   ` = 1/2 . (1 – 1/2011)`

   ` = 1/2 . 2010/2011`

   ` = 1005/2011`

    

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2. Đáp án:

   `1005/2011`

   Giải thích các bước giải:

   `1/(1.3) +1/(3.5) +1/(5.7) +……. +1/(2009.2011)`

   `= 1/2 . ( 1 – 1/3 + 1/3 – 1/5 + 1/5 – 1/7 + …. + 1/2009 – 1/2011 )`

   `= 1/2.(1 – 1/2011)`

   `= 1/2 . 2010/2011`

   `= 1005/2011`

   Trả lời