Let f:R→R, g:R→R, be both differentiable. Suppose that limx→+∞f(x)=limx→+∞g(x)=0, that g′(x)≠0 for all x∈R and limx→+∞f′(x)g′(x)=ℓ∈R. Show that
limx→+∞f(x)g(x)=ℓ
I'm immediately thinking L'Hopital's rule, and investigating when x tends to an element of R. I just learnt this however, how would I go forth to use this (assuming I do actually need to use L'Hopital's rule)?
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