保证真数大于0,有tanx – sinx>0sinx/cosx – sinx>0sinx(1-cosx)/cosx>0可以确定1-cosx≠0,那么一定有1-cosx>0,上不等式两边同除以1-cosx,不等号不变号.sinx/cosx>0,即tanx>0联立1-cosx≠0,及tanx>0可解得kπ...