f '(x ) =[ (x )' ·( x² +1 ) - x · ( x² + 1 )' ] / ( x²+1 )²
f'= ( x² +1 - 2x² ) / ( x² +1 )²
f ' = ( 1 - x² ) / ( x² +1 ) ² ; f '=0 daca 1 - x²=0 rad deriv. x=1 ; x=-1
x -∞ -1 1 +∞
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f ' - - 0 + 0 - - -
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f monot . desc min mc MAX monot. descr
min ( -1 , -1/2 ) MAX ( 1, 1/2)
