分类：教育/科学-学习帮助
问题：(x+2y
回答：(x+2y-1)(x-2y+1)-(x-2y-1)^2 
=[x^2-(2y-1)^2]-(x-2y-1)^2 
=x^2-(2y-1)^2-x^2-2x(2y-1)+(2y-1)^2 
=2x(2y-1)
=4xy-2x