原式=（ x+2 x(x?2) - x?1 (x?2)2 ）× x x?4 = x?4 x(x?2)2 × x x?4 = 1 (x?2)2 ，当x=2+ 3 时，原式= 1 (2+ 3 ?2)2 = 1 3 ．故答案为 1 3 ．
