利用平方差求(x-y+1)(x+y-1)的值
问题描述:
利用平方差求(x-y+1)(x+y-1)的值
答
(x-y+1)(x+y-1)
=[x-(y-1)][x+(y-1)]
=x^2-(y-1)^2
=x^2-y^2+2y-1