f(x)=lnx+x^2-3x,f'(x)=(1/x)+2x-3=(1-3x+2x^2)/x,
令 f'(x)=0,得 x=1,x=1/2.
f''(x)=(2x^2-1)/x^2,f''(1/2)0.
极大值 f(1/2)=-5/4-ln2,极小值 f(1)=-2.