lim(cos1/√x)^2x(x->无穷)

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lim(cos1/√x)^2x(x->无穷)

lim(cos1/√x)^2x(x->无穷)
lim(cos1/√x)^2x(x->无穷)

lim(cos1/√x)^2x(x->无穷)
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/t²
ln(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 -0.5t²
于是
lim(x->∞) (cos1/√x)^2x
=lim(x->∞) e^[2x* ln(cos1/√x)]
=lim(t->0) e^[2/t² * (-0.5t²)]
= e^(-1)
=1/e