`9 : ( x + 2 )^2 + 9 = 9,25`
`⇔ 9 : ( x + 2 )^2 = 9,25 - 9`
`⇔ 9 : ( x + 2 )^2 = 0,25`
`⇔ ( x + 2 )^2 = 9 : 0,25`
`⇔ ( x + 2 )^2 = 36`
`⇔` \(\left[ \begin{array}{l}( x + 2 )^2 = 6^2\\( x + 2 )^2 = ( - 6 )^2\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x + 2 = 6\\x + 2 = - 6\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x = 4\\x = - 8\end{array} \right.\)
Vậy `, x ∈ { 4 ; - 8 } .`