Bài 70 ạ! :)) Bài 71 nx

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1. 70. 

    987 = 900 + 80 + 7

   = 9.100 + 8.10 + 7

   = 9.10² + 8.10¹ + 7.10⁰

    2564 = 2000 + 500 + 60 + 4

   = 2.1000 + 5.100 + 6.10 + 4

   = 2.10³ + 5.10² + 6.10¹ + 4.10⁰

    = a.10000 + b.1000 + c.100 + d.10 + e

   = a.10⁴ + b.10³ + c.10² + d.10¹ + e.10^0

   71. 

   a) cⁿ = 1 => c=1

   b) cⁿ = 0 => c=0
   Chúc bạn học tốt:3

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2. 70 (sgk)

   Ta có:

   `987 = 900 + 80 + 7 = 9.100 + 8.10 + 7 = 9 . 1062 + 8 . 10^1 + 7 . 10^0`

   `2565 = 2000 + 500 + 60 + 4 = 2 . 10^3 + 5 . 10^2 + 6 . 10^1 + 4 . 10^0`

    $\overline{abcde}$ `= a . 10000 + b . 1000 + c . 100 + d . 10 + e = a . 10^4 + b . 10^3 + c . 10^2 + d . 10^1 + e . 10^0`

   71 (sgk)

   `c^n = 1` `(n ∈ NN**)`  `⇒ c = 1`     

   `c^n = 0` `(n ∈ NN**)`  `⇒ c = 0`     

    

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