f'(x)=[(2x-3)(x^2+2x+1)-(x^2-3x+2)(2x+2)]/(x^2+2x+1)^2
f'(x)=(5x^2-2x-7)/(x^2+2x+1)^2=0
x=-1,x=7/5
-10
极小值f(7/5)=-1/24