Tìm x ( x - 5 )^2 = 81

`(x-5)^2 = 81`

`(x-5)^2 = (±9)^2`

`=>` \(\left[ \begin{array}{l}x-5=9\\x-5=-9\end{array} \right.\) 

`=>` \(\left[ \begin{array}{l}x=14\\x=-4\end{array} \right.\) 

Vậy x = 14 hoặc x = -4