求极限:lim[sin(1/x)+cos(1/x)]^x (x趋于正无穷)如题~请写出具体过程

问题描述:

求极限:lim[sin(1/x)+cos(1/x)]^x (x趋于正无穷)
如题~请写出具体过程

原式可化为:e^{limln[sin(1/x)+cos(1/x)]^x}

limln[sin(1/x)+cos(1/x)]^x
=limxln[sin(1/x)+cos(1/x)]
=limln[sin(1/x)+cos(1/x)]/(1/x)
再令1/x=t则化为,则x趋于正无穷,则t趋向0+
limln(sint+cost)/t
利用罗必塔法则:
{(cost-sint)/(sint+cost)}/1 t趋向0+
代入得
=1/1=1
所以lim[sin(1/x)+cos(1/x)]^x
=e^1=e

x趋于正无穷,所以1/x--->0
所以sin(1/x)--->1/x
cos(1/x)------>1
lim[sin(1/x)+cos(1/x)]^x=lim[1/x +1]^x=e

lim[sin(1/x)+cos(1/x)]^x (x趋于正无穷) 令t=1/x,当x->正无穷,有:t->0 则:lim(x->正无穷)[sin(1/x)+cos(1/x)]^x =lim(sint+cost)^(1/t) =lim[1+(sint+cost-1)]^{[1/(sint+cost-1)]*(sint+cost-1)/t} 因为:lim(t->0...