[tex]\sf x^2=81[/tex]
We want to isolate 'x', to do this we have to get rid of the exponent of 2. The opposite of squaring a number is taking the square root. So we can take the square root of both sides to get rid of the exponent:
[tex]\sf \sqrt{x^2}=\sqrt{81}[/tex]
The square root and exponent of 2 cancel out leaving us with just 'x', and the square root of 81 is 9:
[tex]\sf x=\boxed{\sf 9}[/tex]
