很简单的单乘单项式的计算
问题描述：
很简单的单乘单项式的计算
（x-2y)(x+4y) (ab+7)(ab-3) n(n+2)(2n+1) (1-3x)(1+2x)-3x(2x-1)
3ab[6ab-3(6ab-3(ab-1/3a^2b)] 3xy(x-2xy-xy^2z)
(5ab-2)(-3a^2b) (5ab-2)(-3a^2b)
答
（x-2y)(x+4y) =x^2+2xy-8y^2(ab+7)(ab-3) =a^2b^2+4ab-21n(n+2)(2n+1) =(n^2+2n)(2n+1)=2n^3+5n^2+2n (1-3x)(1+2x)-3x(2x-1)=1-x-6x^2-3x^2+3x=1+2x-9x^23ab[6ab-3(6ab-3(ab-1/3a^2b)]= 3ab[6ab-3(6ab-3ab+ a...