Sagot :
[tex]x^2=81\ then\ x=9\ and\ x=-9\\\\because:(-9)^2=81\ and\ 9^2=81[/tex]
[tex]x^2=81\to x=-\sqrt{81}\ and\ x=\sqrt{81}\to x=-9\ and\ x=9[/tex]
[tex]x^2=81\to x=-\sqrt{81}\ and\ x=\sqrt{81}\to x=-9\ and\ x=9[/tex]