f(x)的一阶导数f'(x)=1/x+2x-3
令f'(x)=1/x+2x-3=0
解得x=1或x=1/2
x=1时f(x)=-2
x=1/2时f(x)=ln(1/2)-5/4
极小值为ln(1/2)-5/4