Aplicamos a regra: $\frac{a}{b}\frac{c}{f}$$=\frac{ac}{bf}$, onde $a=d^2y$, $b=dx^2$, $c=x^3$, $a/b=\frac{d^2y}{dx^2}$, $f=\ln\left(x\right)$, $c/f=\frac{x^3}{\ln\left(x\right)}$ e $a/bc/f=\frac{d^2y}{dx^2}\frac{x^3}{\ln\left(x\right)}$