x-y=1,求x²-y²-2y
问题描述：
x-y=1,求x²-y²-2y
答
x=y+1 替换为 (y+1)² -y²-2y
y²+2y+1-y²-2y = 1
答
x-y=1
所以原式=(x+y)(x-y)-2y
=(x+y)*1-2y
=x+y-2y
=x-y
=1