Bài 2 : Tìm x, biết : a, (x – 5)^2 = 36 b, x^2 = 121x c, x^3 = 64x d, x^3 = 1 e, x^3 = -1

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1. `a,(x-5)^2=36`

   `⇔(x-5)^2=(±6)^2`

   `⇔x-5=±6`

   `⇔` \(\left[ \begin{array}{l}x-5=6\\x-5=-6\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=11\\x=-1\end{array} \right.\) 

   `b,x^2=121x`

   `⇔x^2-121x=0`

   `⇔x(x-121)=0`

   `⇔` \(\left[ \begin{array}{l}x=0\\x-121=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=0\\x=121\end{array} \right.\) 

   `c,x^3=64x`

   `⇔x^3-64x=0`

   `⇔x(x^2-64)=0`

   `⇔` \(\left[ \begin{array}{l}x=0\\x^2-64=0\end{array} \right.\) `⇔` \(\left[ \begin{array}{l}x=0\\x=±8\end{array} \right.\) 

   `d, x^3=1`

   `⇔x^3=1^3`

   `⇔x=1`

   `e,x^3=-1`

   `⇔x^3=-1^3`

   `⇔x=-1`

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2. a) $(x-5)^2=36=6^2$

   $x-5=6$

   $⇒x=6+5=11$

   b) $x^2=121x$

   $x^2-121x=0$

   $x.(x-121)=0$

   \(⇒\left[ \begin{array}{l}x=0\\x-121=0\end{array} \right.\)

   \(⇒\left[ \begin{array}{l}x=0\\x=121\end{array} \right.\)

   c) $x^3=64x$

   $x^3-64x=0$

   $x(x^2-64)=0$

   \(⇒\left[ \begin{array}{l}x=0\\x^2-64=0\end{array} \right.\)

   \(⇒\left[ \begin{array}{l}x=0\\x^2=64\end{array} \right.\)

   \(⇒\left[ \begin{array}{l}x=0\\x=8,-8\end{array} \right.\)

   d) $x^3=1$

   $⇒x=1$

   e) $x^3=-1$

   $⇒x=-1$

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