ANSWER :
The values of x are -8 and 8
EXPLANATION :
From the problem, we have the equation :
[tex]x^2-47=17[/tex]Add 47 to both sides :
[tex]\begin{gathered} x^2-47+47=17+47 \\ x^2=64 \end{gathered}[/tex]Take the square root of both sides :
[tex]\begin{gathered} \sqrt{x^2}=\sqrt{64} \\ x=\pm8 \end{gathered}[/tex]