显然x趋于无穷时1/√x趋于0,即cos1/√x趋于1,那么ln(cos1/√x)趋于0而(cos1/√x)^2x=e^[2x* ln(cos1/√x)]令1/√x=t,则x=1/t²ln(cos1/√x)=ln(1+cost-1)显然cost-1趋于0,那么ln(1+cost-1)等价于cost-1再等价于 ...