Find the derivative $\frac{d}{dx}\left(\frac{\cos\left(x\right)}{x^3}\right)$

$\frac{d}{dx}\left(\frac{\sin\left(x\right)}{x^2}\right)$

$\frac{d}{dx}\left(\frac{\cos\left(x\right)}{x^3}\right)$

$\frac{d}{dx}\left(\frac{\left(x^5+3x\right)^4}{cos\:x}\right)$

$\frac{d}{dx}\left(\frac{3}{x^2}\right)$

$\frac{d}{dx}\left(\sin^2\left(x\right)\right)$

$\frac{d}{dx}\sin\left(x^2\right)$

$\frac{d}{dx}\left(\sqrt{\frac{x\left(x+2\right)}{\left(2x+1\right)\left(5x+3\right)}}\right)$