Applicare la formula: $n+x^4$$=-\left(\sqrt{-n}+x^2\right)\left(\sqrt[4]{-n}+x\right)\left(\sqrt[4]{-n}-x\right)$, dove $n+x^4=s^4-81$, $x=s$, $n=-81$ e $x^4=s^4$

Applicare la formula: $\left(a+b\right)\left(a+c\right)$$=a^2-b^2$, dove $a=3$, $b=s$, $c=-s$, $a+c=3-s$ e $a+b=3+s$

Applicare la formula: $\left(a+b\right)\left(a+c\right)$$=a^2-b^2$, dove $a=9$, $b=s^2$, $c=-s^2$, $a+c=9-s^2$ e $a+b=9+s^2$

Simplify $\left(s^2\right)^2$ using the power of a power property: $\left(a^m\right)^n=a^{m\cdot n}$. In the expression, $m$ equals $2$ and $n$ equals $2$