2.计算下列极限:-|||-(1) lim _(xarrow 0)((1-x))^dfrac (1{x)} :-|||-(3) lim _(xarrow infty )((dfrac {1+x)(x))}^2x =-|||-(2) lim _(xarrow 0)((1+2x))^dfrac (1{x)} :-|||-(4) lim _(xarrow infty )((1-dfrac {1)(x))}^kx (k为正整数).