Applicare la formula: $ax+by$$=\left(\frac{a}{mcd\left(a,b\right)}x+\frac{b}{mcd\left(a,b\right)}y\right)mcd\left(a,b\right)$, dove $a=-81$, $b=450$, $ax+by=-81x+450x^4-625$, $ax=-81x$, $by=450x^4$ e $y=x^4$

Applicare la formula: $x\left(a+b\right)$$=xa+xb$, dove $a=-\frac{9}{50}x$, $b=x^4$, $x=18$ e $a+b=-\frac{9}{50}x+x^4$