1/ a. 5 × | -1/10 + 7/15 | – 2/13 × 4 1/3 b. 8^15 × 25^7/ 125^5 × 2^47 c. 8^n ÷ 2^n = 16^2011

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1. Đáp án:

    

   Giải thích các bước giải:

    1,

   a,5 × | `-1/10` + `7/15` | – `2/13` × 4 `1/3`

    =5 x | `11/30`|-`2/13`x`13/3`

    = 5x`11/30`-`2/3`

    = `11/6`-`2/3`

    =`7/6`

   b,`8^15 × 25^7`/ `125^5 × 2^47`

   =`(2^3)^15`x`(5^2)^7`/`(5^3)^5`x`2^47`

   =`2^45`x`5^14`/`5^15`x`2^47`

   =1/5×4

   =1/20

   c,`8^n` ÷ `2^n `= `16^2011`

      `(8÷2)^n`       = `(4^2)^2011`

        `4^n`            =`4^4022`

   ⇒                n     = 4022

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2. `a, 5 xx | ( – 1 )/10 + 7/15 | – 2/13 xx 4 1/3`

   `= 5 xx | 11/30 | – 2/13 . 13/3`

   `= 5 . 11/30 – 2/3`

   `= 11/6 – 2/3`

   `= 7/6`

   `b, ( 8^15 xx 25^7 )/( 125^5 xx 2^47 )`

   `= ( ( 2^3 )^15 xx ( 5^2 )^7 )/( ( 5^3 )^5 xx 2^47 )`

   `= ( 2^45 xx 5^14 )/( 5^15 . 2^47 )`

   `= 1/( 5 . 2^2 )`

   `= 1/20`

   `c, 8^n : 2^n = 16^2011`

   `⇔ ( 8 : 2 )^n = ( 4^2 )^2011`

   `⇔ 4^n = 4^4022`

   `⇔ n = 4022`

   Vậy , `n = 4022 .`

    

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