原式=[ 3x(x?2) (x+2)(x?2) ? x(x+2) (x+2)(x?2) ]× (x+2)(x?2) 2x = 2x(x?4) (x+2)(x?2) × (x+2)(x?2) 2x =x-4，当x＝4? 5 时，原式=4? 5 ?4＝? 5 ．
