First, write 81 as a power, in this case, we know that the square root of 81 is 9, then,
[tex]81=9^2[/tex]
then, we can rewrite the expression as:
[tex]\frac{1}{9^2}[/tex]
since the power is at the denominator, we can write it in the numerator using a negative exponent,
[tex]\begin{gathered} 1\times9^{-2} \\ \end{gathered}[/tex]
Answer:
[tex]\frac{1}{81}=9^{-2}[/tex]
