Tìm x ∈ Z , biết: a) (x – 2) ² – 5 = 20. b) x/3 = 18/2.

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1.  a) `(x-2)^2-5=20`

   `(x-2)^2=20+5`

   `(x-2)^2=25`

   `(x-2)^2=5^2=(-5)^2`

   TH1: `x-2=5`

   `x=5+2`

   `x=7`

   TH2: `x-2=-5`

   `x=-5+2`

   `x=-3`

   Vậy `x=7;x=-3`.

   b) `x/3=18/2`

   `x/3=9`

   `x=9.3`

   `x=27`

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2. `a, (x – 2)^2 – 5 = 20`

   `⇒ (x – 2)^2 = 25`

   `⇒` \(\left[ \begin{array}{l}x – 2=5\\x – 2=-5\end{array} \right.\) 

   `⇒` \(\left[ \begin{array}{l}x = 7\\x= -3\end{array} \right.\) 

   `b, x/3 = 18/2`

   `⇒ 2x = 54`

   `⇒ x = 54 : 2`

   `⇒ x = 27`

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