Find the derivative $\frac{d}{dx}\left(\frac{15}{\ln\left(x\right)}\right)$

Find the derivative

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

Find the derivative

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

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

Find the derivative

$\frac{d}{dx}\left(\frac{5}{x}\right)$

Find the derivative

$\frac{d}{dx}\left(\frac{x^2-1}{\left(x+1\right)^2}\right)$

Find the derivative

$\frac{d}{dt}\left(\frac{\sqrt{t-4}}{tcos\left(t\right)}\right)$

$\frac{d}{dx}\left(\mathrm{sech}\left(-4x\right)\left(1-\ln\left(\mathrm{sech}\left(-4x\right)\right)\right)\right)$