lim(x->+∞) xln(1+1/x)
let y =1/x
=lim(y->0) ln(1+y) /y
=1
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lim(x->+∞) ∫(1->x) [ e^(1/t) -1) -t ] dt /[x^2ln(1+1/x) ]
=[lim(x->+∞) ∫(1->x) [ e^(1/t) -1) -t ] dt /x] . lim(x->+∞) (1/ [xln(1+1/x)] )
=[lim(x->+∞) ∫(1->x) [ e^(1/t) -1) -t ] dt /x ]. 1
=lim(x->+∞) ∫(1->x) [ e^(1/t) -1) -t ] dt /x
等价无穷小的替换啊