摘要：计算或化简 (1) a2(4ab2+6a2b-a2)·(-5a3b4) (2)7x［6x2y-4(xy2-x2y)］ (3)-2(x2-y2)+3(x2-2xy+y2)-4(x2+2xy+y2) (4)2xy［0.75xn+1-0.5yn］-3xy(xn+1-) (5)4ab(-2a-b2)+9a2(-b)-

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