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L'Hospitals Rule

  • Thread starter iNCREDiBLE
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I have an examina soon and I need help with following proof. I don't know TEX that good so I'm attaching a screenshot from word instead.
 

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Suppose that f and g are contiunuous on [a,b], differentiable on (a,b), that [tex]c{\in}[a,b][/tex], and that [tex]g(x){\not}=0[/tex] for [tex]x{\in}[a,b][/tex], [tex]x{\not}=c[/tex].

Let [tex]A:=\lim_{x{\to}c}f[/tex] and [tex]B:=\lim_{x{\to}c}g[/tex].

In adition to the suppositions, let g(x)>0 for [tex]x{\in}[a,b][/tex], [tex]x{\not}=c[/tex].

(a)If A>0 and B=0, prove that we must have [tex]\lim_{x{\to}c}\frac{f(x)}{g(x)}=\infty[/tex]
(b)Also, if A<0 and B=0, prove that we must have [tex]\lim_{x{\to}c}\frac{f(x)}{g(x)}=-\infty[/tex]
 

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