原式= x+1+x-1-(x+1)(x-1) (x+1)(x-1) ? (1+x)(1-x) x = -x2+2x+1 (x+1)(x-1) ? (1+x)(1-x) x = x2-2x-1 x ，当x=2时，原式= 4-4-1 2 =- 1 2 ．
