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(-4x2+6x-8)·(x2)=________;
4x2-4x+1=x2+6x+9
若x2-6x-2的2倍减去一个多项式得4x2-7x-5,则这个多项式是________.
(1)x2-6x+________=(x-________)2;
(2)x2+2x+________=(x+________)2;
(3)x2+________+()2=(x+________)2;
(4)4x2-________+9=(________-3)2.
x2+5y-4x2-3y-1