（1）原式=（4a2-9b2）（-4a2-9b2）=81b4-16a4；（2）原式=x2-4y2+12y-9；（3）原式= x(x?2) (x+1)(x?1) ÷ x2?1?2x+1 x+1 = x(x?2) (x+1)(x?1) × x+1 x(x?2) = 1 x?1 ，当x=2时，原式= 1 2?1 =1．
