原式=lim (x→∞) [ 1 +2/(2x+1) ]^(x+1).令 t =(2x+1)/2,则 当 x→∞ 时,t→∞.且 x =t -1/2.所以 原式=lim (t→∞) (1 +1/t)^(t +1/2)=lim (t→∞) (1 +1/t)^t * (1 +1/t)^(1/2)=e *(1+0)^(1/2)=e.= = = = = = = =...