f(x)=(2*x^3+2*x^2-2*x^2-2*x+2*x+2-2)/(x+1) =2x^2-2x+2-2/(x+1) =2x(x-1)+2-2/(x+1) 其中2x(x-1) ，-2/(x+1)都是增函数，所以f也是增的