Applicare la formula: $\frac{a}{b}$$=\frac{a}{b}\frac{radicalfactor\left(b\right)}{radicalfactor\left(b\right)}$, dove $a=9$ e $b=x^2\sqrt{x^2-81}$

Applicare la formula: $\frac{a}{b}\frac{c}{f}$$=\frac{ac}{bf}$, dove $a=9$, $b=x^2\sqrt{x^2-81}$, $c=\sqrt{x^2-81}$, $a/b=\frac{9}{x^2\sqrt{x^2-81}}$, $f=\sqrt{x^2-81}$, $c/f=\frac{\sqrt{x^2-81}}{\sqrt{x^2-81}}$ e $a/bc/f=\frac{9}{x^2\sqrt{x^2-81}}\frac{\sqrt{x^2-81}}{\sqrt{x^2-81}}$

Applicare la formula: $x\cdot x$$=x^2$, dove $x=\sqrt{x^2-81}$

Applicare la formula: $\left(x^a\right)^b$$=x$, dove $a=\frac{1}{2}$, $b=2$, $x^a^b=\left(\sqrt{x^2-81}\right)^2$, $x=x^2-81$ e $x^a=\sqrt{x^2-81}$