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f(x) -f(2) /x-2 , limita x tinde la 2

Răspuns :

x-2 tinde la 0 plus deci 1/(x-2) tinde la ∞
1) daca f(2)<0 atunci limita este ∞
2) daca f(2)>0 atunci limita este -∞
3) daca f(2)=0 atunci limita e 0

O seara buna!
[tex]f(x)=lnx- \frac{1}{x} [/tex]

[tex] \lim_{x \to \ 2 \frac{f(x)-f(2)}{x-2}=f`(2) [/tex]


f`(x)=(lnx)`-[tex]( \frac{1}{x}) `[/tex]

[tex]( \frac{1}{x}) `= \frac{1`*x-1*x`}{x^2} = \frac{-1}{x^2} [/tex]

[tex]f`(x)= \frac{1}{x}+ \frac{1}{x^2} [/tex]

[tex]f`(2)= \frac{1}{2}+ \frac{1}{2^2}= \frac{1}{2}+ \frac{1}{4}= \frac{2+1}{4}= \frac{3}{4} [/tex]