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=?

x+y=1
(x+y)^2=1
2xy
=(x+y)^2-(x^2+y^2)
=1-2
=-1
xy=-1/2