第1个回答 2013-07-31
原式=(x+y)(x-y)-(x-y)^2=(x-y)(x+y-x+y)=2y(x-y)
第2个回答 2013-07-31
x²-y²=(x+y)(x-y)
所以(x-y) 就变成是一个公因式提取出来
就变成了(x-y) 【(x-y) -(x+y) 】=(x-y) (x-y-x-y)=(x-y) -2y=-2y(x-y)本回答被提问者采纳
第3个回答 2013-07-31
解:
(x^2-y^2)-(x-y)^2
=(x+y)(x-y)-(x-y)²
=(x-y)[x+y-(x-y)]
=(x-y)(2y)
=2y(x-y)