=[-2(x^2 + 1) - 2x+3 ] /(x^2 + 1)
= -2 -(2x-3) /(x^2 + 1)
____________________________
= -2 - 1 /[ x/2 + 3/4 + (13/4) /(2x-3) ]
= -2 - 1 /[ (2x-3)/4 + 3/2 + (13/4) /(2x-3) ]
由于 (2x-3)/4 + (13/4) /(2x-3) ≥ 2√[ ( (2x-3)/4 )·( (13/4) /(2x-3) ) ]
=2√[ ( 1/4 )·( 13/4) ]
= √13 / 2