Find the limit of $3x+1$ as $x$ approaches 0

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

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

$\frac{d}{dx}\left(2x^3\tanh\left(\frac{1}{x^2}\right)\right)$

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

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

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

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