Applicare la formula: $x^2+bx$$=x^2+bx+\left(\frac{b}{2}\right)^2-\left(\frac{b}{2}\right)^2$, dove $b=9$, $bx=9x$ e $x^2+bx=x^2+9x$

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

Applicare la formula: $\frac{a}{b}c$$=\frac{ca}{b}$, dove $a=81$, $b=4$, $c=-1$, $a/b=\frac{81}{4}$ e $ca/b=- \frac{81}{4}$