4.提出3=3lim((1/3)^n+(2/3)^n+1)^(1/n)=3 (底数趋于1,指数1/n趋于0)3=lim(1+3tanx)^cotx=lim(1+3tanx)^(1/3tanx)*3=e^3 (底数(1+3tanx)^(1/3tanx)趋于e,指数为3)