方法一:应用等阶无穷小因为当x->0时,sin2x与2x等阶,sin5x与5x等阶.故lim(sin2x/sin5x)=lim2x/5x=2/5方法二:应用洛必达法则当x->0时,满足0/0型.故可用洛必达法则lim(sin2x/sin5x)=lim(sin2x)'/(sin5x)'=lim2cos2x/(5c...