Evaluate $\mathop {\lim }\limits_{x \to 0} f(x),$ where $f(x) = \begin{cases} \frac{|x|}{x}, & x \neq 0 \\ 0, & x=0 \end{cases}$

$\lim_{x \to 0} \left[ \frac{x \cdot \log(1 + 4x)}{(e^{4x} - 1)^2} \right] = \dots$

The limit of the interior angle of a regular polygon of $n$ sides as $n \rightarrow \infty$ is

Evaluate the limit: $\lim _{x}$ ${\rightarrow \infty} \frac{(\sqrt{3 x+1}+\sqrt{3 x-1})^6+(\sqrt{3 x+1}-\sqrt{3 x-1})^6}{\left(x+\sqrt{x^2-1}\right)^6+\left(x-\sqrt{x^2-1}\right)^6} x^3$

Evaluate the given limit: $\mathop {\lim }\limits_{x \to 0} x \sec x$

$\lim _{x \rightarrow \infty} x\left(\log \left(1+\frac{x}{2}\right)-\log \frac{x}{2}\right) = $