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计算:
(1)
(2)(3x2-xy-2y2)—2(x2+xy—2 y2)
计算:(1) (2)(3x2-xy-2y2)—2(x2+xy—2 y2)
(1)4x3-(-6x3)+(-9x3);
(2);
(3)(8xy-x2+y2)+(-y2+x2-8xy).