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分解因式:a4-1=
(1)(a+b)2c3-7(a+b)c2+12c;
(2)6x-6y-9x2+18xy-9y2-1;
(3)a4+(a+1)2+2(a2+a)2;
(4)(x+y)(x+y+2xy)+x2y2-1.