化简求值(x+1)²-(x-1)(x²+x+1),其中X=根号二 .

(x+1)²-(x-1)(x²+x+1)
=x²+2x+1-（x³-1)
=-x³+x²+2x+2
=-x(x²-x-2)+2
=-x(x+1)(x-2)+2
若x=根号2,则：
原式=-根号2*(根号2+1)(根号2-2)+2
=-(2+根号2)(根号2-2)+2
=(2+根号2)(2-根号2)+2
=2²-(根号2)²+2
=0