设lim[(x-k)/x)]^(-2x)=limxsin2/x,(x→∞).求k.

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设lim[(x-k)/x)]^(-2x)=limxsin2/x,(x→∞).求k.
设lim[(x-k)/x)]^(-2x)=limxsin2/x,(x→∞).求k.

设lim[(x-k)/x)]^(-2x)=limxsin2/x,(x→∞).求k.
lim[(x-k)/x)]^(-2x)
=lim[1+k/(x-k)]^(2x)
=lim[1+1/(x/k-1)]^(2x)
=lim[1+1/(x/k-1)]^[2k(x/k-1)+2k]=lim[[1+1/(x/k-1)]^(x/k-1)]^2k*[1+1/(x/k-1)]^2k=e^2k
limxsin2/x=lim2sin(2/x)/(2/x)=2
即e^2k=2 => k=(ln2)/2

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