Tìm x : ( 2/11.13 + 2/13.15 + 2/15.17 + 2/17.19 + 2/19.21). 924 – 3.x = 1

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1. `(2/(11.13) + 2/(13.15) + 2/(15.17) + 2/(15.17) + 2/(17.19) + 2/(19.21)) . 924 – 3x = 1`

   `=> (1/11 – 1/13 + 1/13 – 1/15 + …. + 1/19 – 1/21) . 924 – 3x = 1`

   `=> (1/11 – 1/21) . 924 – 3x = 1`

   `=> (21/231 – 11/231) . 924 – 3x = 1`

   `=> 10/231 . 924 – 3x = 1`

   `=> 40 – 3x = 1`

   `=> 3x = 40 – 1`

   `=> 3x = 39`

   `=> x = 39 : 3`

   `=> x = 13`

   Vậy `x = 13`

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2. `( 2/11.13 + 2/13.15 + 2/15.17 + 2/17.19 + 2/19.21). 924 – 3.x = 1`

   `(1/11 – 1/13 + 1/13 – 1/15 + 1/15 – 1/17 + 1/17 – 1/19 + 1/19 -1/21) . 924 – 3x = 1`

   `(1/11 – 1/21) . 924 – 3x = 1`

   `10/231 . 924 – 3x = 1`

   `40 – 3x = 1`

   `3x = 40 – 1`

   `3x = 39`

   `x = 39 : 3`

   `x = 13`

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