一、填空题 1．(a+b)(m+n) =______.2．二项式与三项式相乘,在未合并同类项之前,积的项数为________.3．(x+2)(x–1) =__________; (a–3)(a–4) =________.4．(x+a)(x+b) =________.5．(2x–3)(2x+1) =________.6．(3...