f(x)=(x^2+x+2 )/( x-1)
f`(x)=(2x+1)/(x-1)+(-x^2-x-2)/(x^2-2x+1)
f``(x)=2/(x-1)+(-4x-2)/(x^2-2x+1)+(2x^3+2x-4)/(x^4-4x^3+6x^2-4x+1)
当x>1 f``(x)>0 f(x)=(x^2+x+2 )/( x-1)为上凸函数
当x<1 f``(x)<0 f(x)=(x^2+x+2 )/( x-1)为下凸函数
无拐点
f(x)=(x^2+x+2 )/( x-1)图象有点像反比例函数