(1)(x-2y)2(x+2y)2;
(2)(x-1)(x+1)(x2+1)(x4+1)
(3)(x-2y+z)(-x+2y+z)
(4)用乘法公式计算19992-1998×2002.
(5)(a+2b-3c)(a-2b+3c)