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 $a=-\frac{2}{5}$, $b=120$, $ax+by=-0.4x^4+120x+1000$, $ax=-0.4x^4$, $by=120x$, $x=x^4$ e $y=x$

Applicare la formula: $x\left(a+b\right)$$=xa+xb$, dove $a=-3.33\times 10^{-3}x^4$, $b=x$, $x=3$ e $a+b=-3.33\times 10^{-3}x^4+x$