lim(x->∞) xln(1+ 1/e^x )
=lim(x->∞) ln(1+ 1/e^x ) /(1/x) (0/0)
=lim(x->∞) [-e^(-x)/(1+ 1/e^x ) ] /(-1/x^2)
=lim(x->∞) x^2 /(e^x+ 1 ) (∞/∞)
=lim(x->∞) 2x /e^x (∞/∞)
=lim(x->∞) 2 /e^x
=0
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