Hi there!
~
Let's solve your equation step-by-step.
[tex]x^{2} =\ 255[/tex]
Step 1: Take square root.
[tex]x =[/tex] ± [tex]\sqrt{255}[/tex]
[tex]x = \sqrt{255}[/tex] or [tex]= - \sqrt{255}[/tex]
Hope this helped you!