$\lim _\limits{\theta \rightarrow 0} \frac{1-\cos 4 \theta}{1-\cos 6 \theta}$ is equal to

$\lim _\limits{x \rightarrow 0} \frac{\operatorname{cosec} x-\cot x}{x}$ is equal to

$\lim _\limits{x \rightarrow 0} \frac{\sin x}{\sqrt{x+1}-\sqrt{1-x}}$ is equal to

$\lim _\limits{x \rightarrow \pi / 4} \frac{\sec ^2 x-2}{\tan x-1}$ is

$\lim _\limits{x \rightarrow 1} \frac{(\sqrt{x}-1)(2 x-3)}{2 x^2+x-3}$ is equal to