1/2x^2+xy+1/2y^2=8,xy=3求x-y
问题描述：
1/2x^2+xy+1/2y^2=8,xy=3求x-y
答
解1/2x^2+xy+1/2y^2=8
1/2（ x^+2xy+y^2）=8
x^2-2xy+4xy+y^2=16
x^2-2xy+y^2=16-4xy=16-12=4
(x-y)^2=4 x-y=±2