2.计算下列极限.
(1) $\lim_{x \rightarrow 0}( \cos x+x^{2})^{ \dfrac {1}{x \ln (1+x)}}$.
(2) $\lim _{x \rightarrow 0}(e^{x}+e^{ \sin 2x}-1)^{ \dfrac {1}{x}}$.
(3) $\lim _ {x \rightarrow \infty } \left ( \dfrac {x-1}{x+1} \right )^{2x}$.
(4) $\lim _ {x \rightarrow 0} \left ( \dfrac { \arctan x}{x} \right )^{ \dfrac {1}{x^{2}}}$.