f `(x)=[2*(x-1)-2x+1]/(x-1)²=...=1/(x-1)²
avem un raport de numere strict pozitive, => f `(x)>0 => functia f strict crescatoare.
f ``(x)=-2(x-1)/(x-1)²=2/(1-x)
La numarator e un numar strict pozitiv , semnul fractiei e dat de numitor
Pt x <1 1-x>0
x>1 , 1-x >0
x l;-∞..............................0.........1......................+∞
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1-x l+ + + + + ++ + + + l _ _ _ _ _ _
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f ``(x l+ + + + + + + l _ _ _ _ _ _
pt x>1 f ``(x)<0 => f(x) concava
pt x<1 f ``(x)>0 f(x) convexa
