已知x+y=m,xy=n,求(x-y)²和x²+y²的值
问题描述：
已知x+y=m,xy=n,求(x-y)²和x²+y²的值
答
(x-y)²
=(x+y)^2-4xy
=m^2-4n
x²+y²
=(x+y)^2-2xy
=m^2-2n