$$ \mathop {\lim }\limits_{x \to 0} \frac{|x|}{|x|+x^2}= $$

$\lim _\limits{x \rightarrow 3} \frac{(84-x)^{\frac{1}{4}}-3}{x-3}$ is

If $\mathrm{f}(x)$ is continuous at point $x=0$ where $$ f(x)=\left\{\begin{array}{cc} \frac{3 \sin x+5 \tan x}{\mathrm{a}^x-1} & , x<0 \\ \frac{2}{\log 2} & , x=0 \\ \frac{8 x+2 x \cos x}{\mathrm{~b}^x-1} & , x>0 \end{array}\right. $$ then the values of a and b , respectively, are __________