已知x+y=1,x^2+y^2=2,求xy=?
问题描述:
已知x+y=1,x^2+y^2=2,求xy=?
答
x+y=1
(x+y)^2=1
2xy
=(x+y)^2-(x^2+y^2)
=1-2
=-1
xy=-1/2