Answer:
[tex]x=+\sqrt{26}, -\sqrt{26}[/tex]
Explanation:
[tex]\rightarrow x^2-21=5[/tex]
[tex]\rightarrow x^2-21+21=5+21[/tex]
[tex]\rightarrow x^2=26[/tex]
[tex]\rightarrow x=\pm \sqrt{26[/tex]
[tex]\rightarrow x=+\sqrt{26}, -\sqrt{26}[/tex]
