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xRalf

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lim(ln(x+sqrt(x^2+1)), x -> - infinity)

Hello,

how would you solve this limit?

lim(ln(x+sqrt(x^2+1)), x -> - infinity)

I have done these steps lim(ln(1/(1/x) + 1/(1/sqrt(x^2+1)), x= -infinity) = lim(ln((1/sqrt(x^2+1)+1/x)/(1/(x*sqrt(x^2+1)))), x = -infinity)
now I would use l'Hopital rule. But this don't look nice

Is there some easier method?

thanks
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ozo
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xRalf

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Your solution from step 4 looks too complex, where would you take it?

But you gave me an idea.
lim(ln(x+sqrt(x^2+1)), x->-infinity) = lim(ln(x+abs(x)*sqrt(1+1/x^2)),x->-infinity) =
lim(x - x*sqrt(1+1/x^2), x -> - infinity) = lim(x*(1-sqrt(1+1/x^2)), x -> - infinity)) =
lim(ln(x) + ln(1-sqrt(1+1/x^2)), x -> - infinity) = 0 - infinity = -infinity