Applicare l'identità trigonometrica: $\frac{d}{dx}\left(\cos\left(\theta \right)\right)$$=-\frac{d}{dx}\left(\theta \right)\sin\left(\theta \right)$, dove $x=\frac{x}{5}$

Applicare la formula: $\frac{d}{dx}\left(\frac{x}{c}\right)$$=\frac{1}{c}\frac{d}{dx}\left(x\right)$, dove $c=5$

Applicare la formula: $\frac{a}{b}c$$=\frac{ca}{b}$, dove $a=1$, $b=5$, $c=-1$, $a/b=\frac{1}{5}$ e $ca/b=- \left(\frac{1}{5}\right)\frac{d}{dx}\left(x\right)\sin\left(\frac{x}{5}\right)$

Applicare la formula: $\frac{d}{dx}\left(x\right)$$=1$