题目

(1).(x-2y)(x+2y)-(x+2y)^2
(2).(2a+1)^2-(1-2a)^2
(3).(3x-y)^2-(2x+y)^2+5x(y-x)

提问时间：2020-10-21

答案

(1).(x-2y)(x+2y)-(x+2y)^2 =[x^2-(2y)^2]-(x^2+4xy+4y^2)=x^2-4y^2-x^2-4xy-4y^2=-4xy-8y^2(2).(2a+1)^2-(1-2a)^2 =[(2a+1)+(1-2a)][(2a+1)-(1-2a)]=(2a+1+1-2a)(2a+1-1+2a)=2*4a=8a(3).(3x-y)^2-(2x+y)^2+5x(y-x)=...