Applicare la formula: $\frac{d}{dx}\left(ab\right)$$=\frac{d}{dx}\left(a\right)b+a\frac{d}{dx}\left(b\right)$, dove $d/dx=\frac{d}{dy}$, $ab=y\cos\left(xy\right)$, $a=y$, $b=\cos\left(xy\right)$, $dx=dy$ e $d/dx?ab=\frac{d}{dy}\left(y\cos\left(xy\right)\right)$

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

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

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

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