计算(1)(x-1)(x+1) ( 2 )(a-b)(c-d) (3)(3x+y)(x-2y) (4) (2a-5b)(a+5b)
问题描述:
计算(1)(x-1)(x+1) ( 2 )(a-b)(c-d) (3)(3x+y)(x-2y) (4) (2a-5b)(a+5b)
答
(1)(x-1)(x+1) =x^2-1
( 2 )(a-b)(c-d)=ac-ad-bc+bd
(3)(3x+y)(x-2y)=3x^2-6xy+xy-2y^2=3x^2-5xy-2y^2
(4) (2a-5b)(a+5b)=2a^2+10ab-5ab-25b^2=2a^2+5ab-25b^2