x→+0
lim（1/x)^(tanx)
=exp [lim (tanx)ln(1/x)]
=exp [lim xln(1/x)]
=exp [lim ln(1/x)/(1/x)]
=exp [lim (1/(1/x))(1/x)'/(1/x)']
=exp lim x
=e^0
=1