摘要：21．(1)(a2b)3÷(ab2)2×a3b2,[答案]2a7b． (2)(+3y)2-(-3y)2, [提示]运用平方差公式． [答案]3xy． (3)(2a-3b+1)2,[答案]4a2+9b2+1-12ab+4a-6b． (4)(x2-2x-1)(x2+2x-1),[答案]x4-6x2+1． (5)(a-b)(2a+b)(3a2+b2), [提示]原式＝2(a-b)(a+b)(3a2+b2)＝6a4-b4． [答案]6a4-b4． (6)[(a-b)(a+b)]2÷(a2-2ab+b2)-2ab． [提示]原式＝(a-b)2(c+b)2÷(a-b)2-2ab＝a2+b2．[答案]a2+b2．

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