已知x-y=2,求x^2-2xy+y^2的值
问题描述：
已知x-y=2,求x^2-2xy+y^2的值
计算:(2m-n-1)^2
答
x^2-2xy+y^2=(x-y)^2=2^2=4
(2m-n-1)^2
=(2m)^2+(-n)^2+(-1)^2+2(2m)(-n)+2(-n)(-1)+2(2m)(-1)
=4m^2+n^2-4mn+2n-4m+1