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