若x-y=1,则x方-y方-2y-5=
问题描述：
若x-y=1,则x方-y方-2y-5=
答
（x+y）(x--y)-2y-5
=x+y-2y-5
=x-y-5
=-4
答
x^2-y^2-2y-5
=(x+y)(x-y)-2y-5
=x+y-2y-5
=x-y-5
=1-5
=-4
答
x方-y方-2y-5
=(x+y)(x-y)-2y-5
=(x+y)×1-2y-5
=x+y-2y-5
=x-y-5
=1-5
=-4