（x＋1﹚﹙x²＋x＋1﹚－﹙x－1﹚﹙x²－x＋1﹚≥﹙4x＋3﹚﹙x－2﹚

(x+1)(x^2+x+1)-(x-1)(x^2-x+1)>=(4x+3)(x-2)
x^3+x^2+x+x^2+x+1-x^3+x^2-x+x^2-x+1>=4x^2-8x+3x-6
4x^2+2>=4x^2-5x-6
5x>=-8 x>=-8/5